Moisture in distributor cap-Replaced. New plugs/rotor. Recurred. Now what? on 1996 Volvo 850

engine misses only when putting extra load or accelerating. If you accelerate slowly and are careful about pushing it, seems to run fine. Died at stop sign. Would not restart. Towed to shop. Moisture in distributor cap. Replaced that and the rotor. Did ok a couple of days. Happened again. Moisture again. Replaced plugs, wires...bam...did it for mechanic before I got it back. Any insight appreciated.

Asked by for the 1996 Volvo 850