As Duane said, a fluid change may cure, and it's the cheapest potential fix, so start with that. Get 3 qts of "Type F" automatic trans. fluid and an overdrive bottom plate/sump gasket ($8 at Volvo dlr, $6 from IPD). You will see two large hexagonal plugs on the left side of the trans; remove the upper first. This is the filler hole and you need to be sure you can remove it before you pull the plug below it and drain the trans.

Remove the 6, 10mm bolts that hold the OD sump plate. The filter screen may fall out - no problem, it's obvious how to reinstall. Clean the screen, plate and its magnets of all sludge, and make absolutely sure the old gasket is completely removed from all surfaces. Reinstall the plate with new gasket and do not overtighten the 10mm bolts. Fine threads in aluminum = easy to strip.

With the left side of the car raised (safely) higher, fill the trans through the upper hole. This overfills the trans a little. Although the OD must be separately drained, it will fill with the trans. I use a length of clear tubing and a small funnel and fill from the engine compartment. Very laborious and messy - an alternative is to get one of those little plunger gear oil pumps and work from under the car. When fluid runs out of the hole, you're done. Might solve your problem for ~$12.
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Bob (81-244GL B21F, 83-244DL B23F, 94-944 B230FD; plus grocery-getter Dodge minivan, MGB, and numerous old motorcycles)