1992 engine seals

does ANYONE know how much it would cost to replace the engine seal(s) in the 1992 continental? about 2 months ago my parents continental started running rough. it got to the point where it sounded like a 25yr old diesel. that day the car stalled like 3 or 4 times. black and white smoke came from the tailpipes and eventually the engine itself started to smoke. in the intervening months it hasn't been driven much except to move it around in the driveway to get ready to be sold. 2 days ago my dad got it jump started and it started right up and drove reasonably well all things considered. it has oil in the crankcase however the oil pan screw apparently rusted so bad over the winter that the oil could not be changed after winter. my dad was told by a mechanic that it very likely was the engine seal(s). apparently these are a big problem area on these 3.8L motors. any help would be TREMENDOUSLY appreciated since nobody wants to buy the thing and we will be moving from upstate new york to the birmingham, al area as soon as we can sell our house. thanks to all who can provide advice and assistance.