2001 Subaru Outback 100000 miles

2001 subaru outback with a 3rd cylinder gasket leak into the combustion side. No oil found in the coolent and no coolent found in the oil. Car sputters when started and blows a little bit of white smoke then clears up and runs fine. I've been quoted between 2500 and 3500 dollars to fix. Are there any sealants out there that I could try that's not going to gum up the engine, valves ect.

Thanks, Darryl