S13 Sr20de Auto - No Drive, Need Advice

[BLSTIC]

Ok so we picked up this S13 for a song because the gearbox doesn't work. The car was confiscated for unlicensed driving so I know it was working when it was last switched off (6 months or so ago)

If we leave it for a few days then put it in reverse it jolts (ie goes into gear) but won't drive for long at all (a matter of seconds).

Today I dropped the pan and aside from the fluid being really old nothing looked out of place, and the filter still flowed. The fluid level was ok in park with the engine running, but I'm not sure any of the fluid is actually getting anywhere in the trans (otherwise it would work, no?).

So has anyone experienced this problem before? What did you need to do?

I can drop the valve body off and pull it apart for inspection, but I would rather not.

thanks

Ben