This is my first post here, but I've been collecting Soviet watches for about 2 years now, and only recently begun working on them. I've done plenty of precision work in the past in various fields, but watches are new to me. I've fixed a handful of Amphibias, but mainly easy adjustments with little mechanical issues. I picked this watch up about a month ago for very cheap, and it's beautiful if not a bit small. It runs fine, winds easy, but gains time like none other. My main leads from previous research are a gunked hairspring or magnetism. My question is pretty straightforward I suppose. How do I go about determining the correct direction to head in? I feel 15-30 minutes of gained time is significant. I can post movement pictures but seeing as it's my first post I don't believe I can. I will link a photo from mroatman's page as it's nearly the same watch but with a stainless or plated case instead of gold. Any lead in the direction I need to head is most appreciated. Thanks in advance.
The watch in question, only mine has an identical case in silver color.