I bought a used '95 Turbo Wagon that had 3 sources of oil leaks - all found and fixed myself. There's two likely causes of the leak you described.

1. The turbo return line (as someone else had responded). The bottom of the return line goes right in above the oil pan. The original o-ring shrinks and the leak starts. Volvo has upgraded the material from a black rubber to a heat resistant green and it's a cheap part. To replace it, you'll have to take the two bolts loose from the turbo housing and the one bolt that connects the o-ring end. Get a turbo oil line gasket also (cheap) and change that out at the same time.

2. Oil dipstick tube. The o-ring at the bottom of the oil dip stick tube is like the one for the turbo return line - same fix. Also the dipstick itself has an o-ring that should be replaced.

If these don't work post again and I'll get into my other leak repairs...

Good luck - Scott '95 855t /'88 745gle