Hi gary, i haven't worked on a SL500, but i do remember not having much room in my 97 E420 either.

there are a few things you can try,

1. get a product called "pb blaster" and spray liberally on the bolts

2. jack the car up or put it on ramps, and then use a 25" breaker bar.

3. use a 8" ratchet and a floor jack to break the bolt loose. does that make sense? rest the ratchet on the floor jack, and then raise the jack very slowly until the bolt comes loose. this outta do the trick.

4. last resort, you could rent an impact wrench (at least 300 ft lb torque) and carefully break the bolt loose.

g/l, and be sure to loosen the fill bolt first!

__________________
Current cars:
2001 MB E55 AMG
2003 Honda S2000
2000 Honda CRV

Gone but not forgotten:
2004 BMW 325i 5sp sport
1999 BMW 540i sport
1997 MB E420
1995 BMW M3 coupe