I own a 1997 Cadillac DeVille S&S 6 door Formal Limosine with only 19,000 original miles on it. I love this car. But it has issues. Low coolant error viewed on dash and i filled gas tank full parked it for 2 months only to find out it had only 6 gallons of gas in the tank. I live in a rural area and no one syphoned my tank..I also need to know what is the very best way to repair head gasket. I remember this company that makes special head gaskets and coarse threaded special head bolts in a kit form but I do not remember the name or website of that company. Please help me!

 

IDK what to tell about missing gas. It had to go somewhere, if it leaked out there would be a hell of an odor and a puddle.
Coolant - pressure test cooling to see if it's just a external leak. Have a CO test done on cooling to verify CO is present in cooling meaning probable blown head gasket(s). Engine should come out to replace head gaskets. Engine is supposed to come out the bottom. It is possible to do head gasket repair with engine and transmission still bolted together. As far as the we can do it better than GM kits IDK haven't seen them advertised in years. Some techs will want to "time-sert" block when they replace head gaskets whether needed or not. It is not advised to try to change them while engine is still in car. Good luck.