The tire problem sounds like either the people mounting the tires are fools - or it isnt tires at all, but something else.

The key/lock issue is hard to say - any dealer should be able to sell you a compatible key (or put a new battery in the one you have - remember, that function of the key is battery operated). It can be the central locking pump as well, but problems with those are kinda rare.

The car is a Mercedes, so taking it to Chrysler is usually a pretty bad move. Most MB dealers won't like working on it, either. I use one of two local independent shops that specialize in Mercedes products for anything I cant do on my own. You did not indicate where you are and that makes it hard for us to suggest where to go. For example, here in the Atlanta area, Buckhead Imports is the service facility of choice for most of us - even those of us as far away as Nashville!