1992 Mercedes 300 TE wagon - 150k miles

Symptoms:

1. When cold the transmission delays shifting and then shifts hard. Once warmed up it shifts perfectly with no slipping

2. When putting in reverse - cold or warm it takes a long time to engage - up to a minute. Once in gear it works fine. The time to shift into gear Revving the engine the car moves slowly and then catches and works fine. Each time it is shifted into reverse it takes the same amount of time to engage.

The Mercedes Dealership says I need a new transmission. This has been confirmed by a couple of transmission shops. Is there any other options and where can I get a rebuilt transmission?

One other issue the Engine Check light came on at 150K miles. Is there a way to turn it off.

Thanks

Dan