I have a small but aging collection of LF lenses that have mechanical shutters. Some of the shutters are getting slow and even some are getting stuck. How easy it it to clean and lube them? Are there resources to learn how to service them? I don't want to take apart a shutter and ending ruining it. Any suggestions? Maybe just send them in? I'm a DIYer, but I don't want to get in over my head. Thanks in advance!