Pssssssssst................. hey Buddy! Wanna CHEAP lens cap for that Summitar?
I, too, was in need of a couple of caps for a Summitar and a Canon Serenar that looks for all the world like a Summitar copy. I found that an FSU J-8 lens cap that's smooth inside (some have ridges) will fit perfectly when a ring of 1mm felt is placed around the inside lip. Not only does Jon Goodman's seal kit have 1mm felt but it's also self-adhesive. Works like a champ!!
Alex-Photo sells the plastic caps for $1.25 each with shipping cost at $7 for up to 20 caps.
Anyone who thinks using FSU caps on Leica lenses is the act of a heathen can go pay $20 or more for a cap. Not me. Caps are too easily lost.
Walker