Edit: this is all U1, the OP is asking about U2..../Edit
I ordered mine new, from outside the USA. I don't think anyone went inside mine after assembly, until I got it. The only exception being to remove the restrictor plug (if they come with them by default). The screw that captures the restrictor plug (if one is installed, behind the screw) is on the right side of the rear block. Another easy place to look (there's an o'ring there).
I've had mine partially apart (removed and replaced regulator). There was debris (metal, gunk, etc.) inside, every place I looked along the way to get the reg out. So it could be a guessing game. The reg's bleed hole in the rear block is on the same side as the restrictor plug/port cover mentioned above.
Some will say soapy water. Some will say absolutely do not use soapy water, and use gas leak detection solution. Might be worth getting some.
Sorry, I know this doesn't really answer your question about common leak points. Mine never leaked (yet, surprisingly....knock on wood). But I'm having other issues with it.