transmision service question 1981 300SD and trans slipping
 

So this 300SD I picked up, had a real bad slipping trans. First thing I did was top it off (over 1qt low) and it instantly became drive able in first gear only, but still slipping trying to go into 2nd and 3rd gear, not slipping at low speed in first.

I have it up on stands with the fluid drained, pan off etc to replace the fluid and filter.

This has cured transmission problems with my other cars in the past where a dealer or transmission shop said the trans was toast.

So the questions:

Is there a compatible fluid type available from the local auto parts store that is proven to work? (the parts store guy recommended synthetic multi fluid that meets all current dextron and mercon requirements)

Next, while I have the pan off, is there anything I should change in the valve body, such as springs, seals or piston components that may be worn.

Basically I would like to change anything that is not too expensive, and that can be done from underneath without pulling the trans.

Thanks

A new B2 piston may firm up the 1-2.

Thanks, I will pick one of those up,

anything else???