I would not mess around with your local gunsmith, especially if he says HKs are a pain in the #$# to work on. Send it to James, his work is second to none. He probably can put it back together with a blindfold on!! He does awesome work.
I don't recommend completely disassembling the VP9 unless you know exactly what you are doing. I attended the factory authorized HK VP9 armorer's course several years ago. And, I have to say, it wasn't an easy one. There are a lot of parts that require special attention to detail during the disassembly and assembly process. The operator's/maintenance (armorer's) manuals are 140 pages long and extremely comprehensive. As a side note, on page 8 section 2.4 of the armorer's manual, it states the following: Exclusion of liability and warranty. Heckler & Koch GmbH accepts no liability and provides no warranty for incidents arising from: "Modifications, attachments to or conversion of the weapon (VP9) without the express written consent of Heckler & Koch GmbH or use of accessories or spare parts from other manufacturers without the express written consent of Heckler & Koch GmbH." So with that being said, proceed with caution!