1994 S500 Transmission

[dbs600]

Hello:

I am the owner of a 1994 S500 and over the past year I began experiencing transmission problems. First there would be a delay shifting into reverse (2 seconds), then the delay gradually increased (5 seconds, 10 seconds, etc...), then to get the car to actually move I would need to give it gas with the vehicle sometimes jerking backwards. As of two days ago the car no longer goes in reverse. I press the gas, but all that happens is that the engine revs - no wheel movement. Otherwise, the forward gears work fine (although, I have noticed a little bit of a hard shift from first to second in recent days).

I have been searching various forums and have determined that I should either have it rebuilt or have it replaced. However, I would like to clarify the following:

1. Which transmission does my car use - the 722.2 or the 722.3? What are the differences between these?
2. Is the dealer quoted price of $6,500 for a replacement too high? Should I get a second estimate?
3. How much should I expect an independent shop / tech to charge?
4. What would a "valve body mod to increase the fill rate of the reverse clutch pack" do in my situation? Does this require transmission disassembly?
5. If the dealer replaces the transmission would it cause added stress on the engine - and / or cause it or other components to fail sooner?
6. Would it be possible for the dealer to replace the transmission with the 5-speed version of the 1996 - 1999 W140's?

Last, is there something that I could / should have done to prevent this? I have owned the car since new and cannot understand why a pre-95 Mercedes with less than 100k miles should experience a transmission failure.

Thank you very much.