I've changed the fuel filter on same yr/make/model twice, once with the gas cap left on; once with it off. I didn't seem to make alot of difference as far as how much fuel flowed downward once things were loosened up. It's not the cleanest maint. task, but not too bad.
I did remove the battery ground strap first and back the car up on ramps for ease of access. Be sure to change the copper O-rings. If you encounter leakage after you put it back together, snug down the connections some more. Things need to be fairly snug.
1991 300-SEL - Model 126
M103 - SOHC
James Madison - Oppressors can tyrannize only when they achieve a standing army, an enslaved press, and a disarmed populace.
Liberty Firearms Training - After years of trying to regulate California criminals with a never ending stream of gun control laws they have still not given up with the belief that if they make something a crime that criminals will miraculously start obeying the law.