When Mason & Sullivan went out of business in 1992 I purchased the plans, dial, hardware, and movement needed to construct their “Crystal Regulator Clock”. That was 28 years ago and now that I am retired I have finally got around to building the walnut case from scratch. The movement was stored in its original packaging all those years and before installation I did lubricate it as best I could with a clock oiler. So far so good, it keeps excellent time, losing less than a minute over 6 days. But that 6 days is the problem, when fully wound the clock consistently stops then, even though it is an 8 day movement. I infer from that that the mainspring somehow got gummed up during those 28 years of storage, such that it is unable to provide the full power. So the question becomes what can be done about it? The original movement is a M&S 3396X, with polished brass plates, made by Hermle. A new replacement movement (Hermle 131-080, 23 cm) is available, but that one has the standard Hermle dimpled plates instead of the polished ones, and since the glass sides of the clock make the movement highly visible a polished appearance is preferable. My question (as a case-maker, not a clock repairer) is as follows — would the cost of having a professional fix the mainspring (assuming that is the problem) in the original polished movement be competitive with the cost of a less-than-ideal replacement? Thanks for any help.