I've used Super Lube with Syncolon (PTFE, aka "Teflon") for about 10 years now, and it's been perfect for almost all airsoft use, from all gearbox parts to GBB's. The viscosity has the perfect balance of low resistance with "sticking" power, and the oil base with PTFE has really good lubricating properties.
www.super-lube.com
After doing gunwork for other people for almost 8 years, I'm finally coming to the end of the original 3 oz tube I'd purchased, so I'm looking to buy more of this awesome stuff, but have no idea where to get it.
I had an easier time finding this stuff before, but it seems like it's impossible these days. Does anybody know of anywhere local to find this?