I could be incorrect here, but I believe the stories on synthetics making leaks worse is from the days of Mobil 1 0w-30. Now that they have more "conventional" multiweights, the problems don't occur as often...

For changing the transmission fluid... Not a big deal at all. Get a kit from Partshop. Wait for it to arrive... Then do a search here to get info, it's been done before. You MUST drain the torque converter, so I start there (if you can't get that to work, you are out of luck...). Really it's the only pain. The biggest thing to remember is to be absolutely meticulous - keep ALL foreign matter out of the pan.

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Bill Streep
San Antonio
'57 190SL (toy)
'08 S5500 (mine)
'09 CLK550 (wife's)
'06 SLK350 (daughter's)
'11 GLK350 (daughter's)
'03 CLK310 (spare)