Ok, yeah, i had to go to MBUSA.com to find out. 1998 is actually the first year they rebadged it the CL.
The whole prospect of what you are considering seems ridiculous to me, swapping trannies back and forth. Take the tranny out, repair tranny, reinstall tranny.
The front pump I am referring to is the front pump. Yes, more than likely it is the sorce of the growling and is also what is causing the shifting problem. I'd have a transmission specialist familiar with 722.6 (probably a job for a dealer) do some quick diagnosis on it.