What do I really need to repair/change?!

[sanchezc]

My 1991 300 SE has 110,000 miles. Depending on what MB specialist or dealer I ask I get different opinions on the yet to do's to bring it to its "nominal" shape. So I would like other opinions to try and reach the right conclusions. Here is the detail:

* My transmission rattles when backing up in the morning, and Reverse takes about 3 seconds to engage. Forward gear changes seem however fine. Some tell me that I should overhaul it sooner than later, others that I'll get ample warning signs before getting stranded. What's your experience?

* I had understood from reading this forum that the M103's timing chain was short enough that it's replacement wasn't really needed. I am however told that I should replace it in 10,000 miles or so, if only as a prevention: did I misunderstand what I read here?

* My power steering fluid was recently replaced, and ATF was used instead of proper power steering fluid, which I am told is fine on my car: true? Due to a slow leak, I had bought some proper power steering fluid (from FastLane, of course ): if the leak persists, will I be able to refill the ATF with the power steering fluid, i.e. are they compatible?

* My exhaust had a crack which was welded. I am told that the catalyst may no longer be doing its cleaning job properly, and that, if I want to stay OEM as I'd like, I'll need to change the whole system at a cost of $2,800, parts only. Is there really no way to change only the parts which are failing?

* I am also told:
+ by one specialist that my O2 sensor is working fine, and that the spark plug wires hardly ever need to be changed,
+ by another that my O2 sensor is original, made for 60k only and that I should change it, as well as my spark plug wires to fix my slight vibrations and surges at idle (which were not helped by changing the spark plug caps/connectors).

* Some hear "whistles" from my fan, air pump and idler bearings, some don't: is there a typical mileage at which these bearings should indeed be changed?

* Some tell me that my shocks and engine mounts are fine, some that I should change them: what are some reliable symptoms?
+ Could weak engine mounts explain the slight vibrations at idle (if not the --again slight-- surges, and even though L6's are supposed to be "ideally balanced")?
+ The rear of the car bounces more than once when pushed down by hand.

* What are the "rear control arm bushings"? Some say they are noisy, others that they are fine.