Moreover, what year did Cadillac fix the Northstar head gasket problem?
2002
Additionally, how reliable is the Cadillac Northstar engine? You should do a search as this has been discussed many times.. As long as you maintain the engine, particularly the cooling system, the Northstar is very reliable for hundreds of thousands of miles. Personally, I had 110,000 on a 1995 Cadillac Eldorado Touring Coupe and it still drove like brand new.
Secondly, what year did they fix the Northstar engine?
2000
What is wrong with Cadillac Northstar?
Head gasket issues
Many Northstar engines became well known for their tendencies to experience head gasket failure. The issue manifested itself not as a "true" head gasket failure, but as a head bolt failure.