We used I believe Barrs leak that comes in the silver bottle.Had a few customers with GMs infamous 3.1s that had intake and a few that had a head gasket leak.They didnt want to spend 1K or more to fix them.One guy drove to Pitt from here and wanted a month out of his van.He was still driving it like 4 months later.It costs like 30 bucks for the bottle and you just add it no flushing.It wont fix something major but has worked on the smaller leaks we had.Not a permanent cure but might get her thru for a while.Rocky