sounds like your car was messed with ( MODDED) by someone that had no idea what they were doing.
First the problem with the oil filter is that it is probably installed wrong. There is a ' THREAD" showing how this is done properly. Buy oil and filters when they are on sale, I usually pay $4.99/qt and use "Fleese filters" Ebay $6-9.00 Each.

The rear end whine, may be from low grease level, but putting it in now is probably of no use. Try it though, whine may not be too bad. Sounds like it will need to be replaced. Go to" The Crossfire Shop" he can get a good rear end at a decent price, maybe he will have mercy and let the part go cheap.

The fuses being welded in , is from way to much current going through, Contact 180 on the forum to see if he has any ideas. Sounds like someone tried to install a different radio or some other accessory and shorted it out on the install and fried some wire. You could still have a big problem waiting to happen. May be able to buy a wiring harness from "The Crossfire Shop" to replace either all or part depending on how bad it really is.

I just put "General G MAX A3s" on my car, $1,000 mounted, balanced, TPMS rebuild kits, tax, etc, installed. Not cheap, but you don't want cheap when you are running 120MPH or so. Did that when I was young and dumb, but not anymore.

Last but not least find some of the Forum members that are near you, they are always glad to help. That's how i learned to change my oil the first time. Only take your car to a really good shop that knows Mercedes, stay away from dealers, Chrysler or Mercedes, they love to see you come through the door. Most of them don't practice safe sex, so be prpared to get stuck BAAAAADDDDD.

I am without a clue on your gas tank problem, but I bet it has been modded for some reason and really messed it up. Get another tank and filler neck from "The Crossfire Shop". Run out all the gas before you remove it and make sure you are a very long way from any ignition source, a long way!!! This can burn down your house or garage and fry you up too, be very careful. You can do almost anything on the car yourself, but you have to learn how to do it first.

Hope I have been of some help, enjoy the car!!!

The guy that owns "The Crossfire Shop" is a forum member and a good guy, I know he will be a big help to you