I've a 2013 GL450 with 20K miles on it. My driver side rear tire has a nail near the side wall. MB dealer said he can't fix it for safety issues, drove to discount tire and he offered to fix it for free but he unmounted the tire to show me the nail which was unfortunately in the direction of the side wall and termed it Non-repairable . Almost all my tires have 5/32 tread remaining and Discount tire recommend changing all 4 tires after speaking to the MB dealer over the phone. Obviously I wasn't prepared to change all 4 tires just after a year of lease (Bought in June 2013). However, MB dealer is recommending changing a pair of tires (asking 700 installed for 2 tires).

Also to save some $$, discount tire suggested shifting over to 285 50R20 (OEM is 275 50R20). Will that change anything and also will MB accept it at lease return?

Please suggest! I cant see my GL handicapped with that skinny spare Thanks!

I used 285/50/r20 tires on my previous GL and it worked fine. The car actually looks and handles better IMO. MB accepted my Bluetec with these regular tires ( originals were Run Flats) as a trade in with no issues, certified it and sold it in 3 days.
On the other hand - I had the same issue and my MB dealer said it's not repairable. I went to our local independent tire shop and they fixed it for $20. Never had an issue with that tire again.

I would suggest you don't have two different tire sizes on a 4matic.

Yes - sidewall punctures are "non-repairable" - in this case choosing to replace two "same size as original" I would run those on the front.

You can turn a leased vehicle on flat tires if you want ...

And they won't charge you for it? How about tread wear? Couldn't tell if you were being sarcastic or not.

I agree - sidewall damage means a new tire.

I had the same issue of a sidewall problem on my GL350, but had closer to 25k miles. I was within a few months of having to replace them so ended up getting all 4 new. I put the Perelli's on again.