we've tried,

Kroil, I wasn't impressed

PB works but stinks

A couple brands of the freeze off by different companies, Rip OFF

Liquid wrench so-so

A friend at another shop gave me a can of Free all to try and it is the current favorite in the shop. it has consistently worked where others did not. it is not readily available so I buy it online by the case

http://www.alliedelectronics.com/FS16.html

twocents