Warning Light On problems of the 1998 Oldsmobile Silhouette

I have had numerous problems with this car since I purchased it. The power sliding side door has benn repaired 2 or 3 times and still works intermittently. The headlights have been repaced once and repaired once and they now have water inside causing the lights to perform poorly. The air bag warning light was repaired at a cost of $80 due to corrosion causing the light to come on. The check engine light comes on if you drive over 100 miles then eventually goes off. Now, the major problem is that I have been told by my mechanic that I have a blown head gasket or cracked block which is causing antifreeze to leak into my oil. There is a possibility that the engine needs replaced. I noted numerous instances of blown head gaskets on gm message boards. This seems to be an ongoing problem. I contacted gm and received no offer of help. The request # given to me was 06214553. This is the 7th or 8th gm vehicle I have owned and have never had any problems. This one has been nothing but a problem. Does this classify as a "lemon"? any help would be appreciated.