My rear tires wear on the inside.

Springs are sagging or suspension is bent. Could be worn bushings causing components to be out of position. Springs support the weight and the shocks dampen the bounce so he doesnt keep bouncing- if it does then you need shocks. The sagging indicates something else is wrong.

can be anything have a 4 wheel alignment done ---problem for excessive tire wear --out of balance --improper tire for vehicle -chamber to much/to little- air under / over inflated -abuse -bad shock/strut-bad hub/axle --suspension alignment / worn /damaged

sounds like you need to have the rear suspension checked for any damage and then a 4 wheel alignment to check rear angles.

if it has independent rear suspension then have the suspension rubbers checked and replace if necessary. Next for all wheel alignments it is essential that the rear end is aligned first to stop this tyre wear before the front wheels are aligned . IF you have leaf springs at the rear check for axle alignment and broken centre bolts or worn rubbers at the centre bolt mounts.

I replaced the rear struts, when removing i discovered one was totally bad, they didn't seem bad from testing and recovered quickly when pushing on the bumper, but were bad. after replacing my rear tire wear is even after 5k miles. mine were wearing from inside to outside too.

I am not an Mercedes expert, but if your rear axle is not solid from one side to the other, you have one of a number of hinged floating rear axles. These may simply require an alignment, just as the front end requires.

With excess wear on the inside track of the tires, the inside of the tire is pitched down lower than the outside edge. Most rear tires are set to run level or slightly pitched to improve handling.

If your rear assembly is not adjustable, the connecting bushings are worn on the linked suspension or the rear axle bearings have excess clearance.

Go somewhere to have a 4 wheel alignment, not to be confused with 4 wheel drive.

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Have the rear suspension checked and fixed and an alignment done. If someone did this already take it to a different shop

I'm guessing the lower ball joints are shot. This will cause the tires to lean in on the top and and wear the inside of the tire. I could be wrong! Try jacking the front wheels up and support the vehicle on jack stands, now grab the tire top and bottom and try to rock it in and out. If there is movement, you will have to have someone watch to see what is moving, while you rock it. If it's the ball joints, they will need to be replaced before you can align it. This can be spendy, there's a lot of labor involved.

Fishtailing comes from two things...First, all tires are not equal when on wet roads. There is a distinct difference between brands tires and even different tread patterns within the same manufacturer. To find the best tires for your vehicle, you need to experiment with different brands etc. (also look to see what other people are using and how well their vehicles handle.) Worn tires regardless of make will tend to loose traction as well.
Second, vehicle weight distribution (pertaining to weight actually pressing down on each individual wheel). Adding weight to the vehicle by loading up the back with heavy items sometimes helps but will destroy your rear suspension. I use a "non-traditional" fix for this by adding two 20lb flat lead weights to the rear axle (using two longer "u" bolts, one on each side, to fasten them under the spring, behind the brake assembly) With additional 20lbs at each rear wheel, the weight is not on the suspension but adds 40lbs to the rear axle weight, low, where it enhances traction and changes roll center in a good way You may also benefit by adding heaver sway bars to prevent "wheel lift" during cornering (both front & rear must be matched).
I don't know how aggressively you drive, but if you take it a bit easier on turns this will help as well. Driving in 4wd will obviously wear the 4x4 components faster than not using them, but using anything will eventually wear it out! (your vehicle would last a lot longer if you kept it in the garage and didn't drive it.) Use it when you need it...that's why you bought it! It dosen't rain every day!
Hope this helps you ...

Unless there is noise or play when cornering sharply at low speeds (parking), the CV joint / boot is still ok. The joint does need grease in there and the rubber boot fitted properly very soon.

As the suspension is set, the axle does little more than provide drive. It doesn't affect toe-in or camber angle.

Camber angle (vertical tilt inwards) is a product of the suspension design, and often cannot be altered.

Weak front springs can also throw this angle out, as the vehicle sits too low.

Toe-in (forward point angle) can and must be set accurately, or you will skid about in wet weather depending which tyre grips more.

What is most important to you, is the tyre design, tread width and outer radius. Also the tyre pressures MUST be mid limit when cold on the front - otherwise excess wear will result.

Having tyres with a large contact area that are too rigid on the front will increase wear to the insides.

Also, it is good practice to rotate the tyres to even-out wear. Usually front tyres move to rear axle, and rears swap sides to front axle. If wear is uneven, pop them off and turn around before refitting. Some tyres you cannot do this with.

If you choose a tyre with a harder tread compound, or ones with "C" at the end of the code, these will again last a lot longer.

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