My v.g. condition (but possibly somewhat old) Nisshin runs a few minutes and then stops. The train appears to me (novice) to be underpowered, so I suspected the mainspring (the fork just didn't seem to have enough oomph, but what do I know...). The lock and drop also look good (same caveats again). The clock repair guy who gave it to me also commented that it looked underpowered to him (he was closing up shop and moving, and was giving things away he had no time or need for...Keith Clayton-Kastenholz is a really nice guy and has been very helpful to me!) When I took it apart there's no slot in the barrel cover, so I'm not sure how to remove the mainspring without damaging something. I've read you whack the arbor to push the cover out, which seems scary to me. The pivot holes look good, albeit a bit oily, but very little dirt. I don't think it ran much before it was given to me. I'm wondering if the mainspring is good but excess oil is the problem? Should I clean and put it back together and hope for the best, or is removing and checking the mainspring safe and easy enough that I should do it now when it's already open?