1996 Chevy Camaro Engine failure

Should I get a re-manufactured engine installed? Here's why: I retired my (bought as new) 96 Camaro (117,000 miles - V6) two years ago from daily driving. Because it still looks like new, my plan was to rebuild as needed later, for fun and use as a weekend hobbie car. My current serious problem started showing as a lack of power especially from 1st to 2nd gear and/or when pushed up a hill--power so low that it feels more like 3rd, or overdrive. Car never acted like it didn't want to start, or ever wanted to die. Didn't have it checked till last year since I had a newer car to drive. Dealership didn't keep it but a couple of hours and said they didn't know what was wrong--don't think they drove it either. Turns out I had to sell the newer car now(out of a job) and put the Camaro back in daily service at least for this year, so took it to different dealership--took svc mgr for a ride and he said he couldn't tell what was wrong, but had no suggestions or leaving it to try to find the problem.
I took it back few weeks later(this week) and I said since they don't what to check, to just put in new plugs (originals were still in use) and wires and new a/c compressor, and I would check how it drove. They called later that day to say when taken for a test drive after repairs, the engine froze/quit--they started it back up and says now makes a horrible noise. Told me must break down the engine to find problem but also talked about a new(re-furbished) engine. Now they say the crankshaft is scored from lack of lubrication/condensation. This car has always started and has never broken down. Should I let them put in a new engine? Total cost for everything to do:$6,000! I'm already in debt to them for the a/c, plugs and wires. ($1,500) on a dead car.
History: Bad backfiring when first bought.--They didn't know why-car seemed to recover/ Not long after:slight cutting out when pushed and lack of power--they didn't know why and car seemed to recover / 1999:Spark plug recall same week car was in the shop 3 days for lack of power/cutting out--so that time they knew what to fix due to the recall / Also an oil leak from about' 98 that got much worse, and after 3-4 visits they never fixed--so I stupidly got tired of trying and gave up, but never let the oil get low / Car overheated once at about 90,000+ miles and cooling system parts were replaced /
Ever since, car has run warmer than it ever did before at idle in warm weather or if driving slow traffic (never overheating, though). But techs kept telling me car was running normal temp. I also asked a few times in recent years if the oil leak could ever harm the engine and I was alway told no. Has all this lead to this engine failing now? This dealership also checked fluids at entry. The car was not clicking, clanking or making any odd noises before. Am I totally responsible for repair costs? What should I do?
Out of work and didn't no there was a charge for this inquiry--so whoever would like to respond--thank you.