Yes sew ups or tubular or "singles"as we called them are repairable.I have an old friend who repaired them for years.He can no longer do it due to the effects of a stroke but he routinely did 15 to 20 a night in the 70's and early 80's.His method for finding the location of the puncture and stopping the tyre from going out of shape was to mount them on to a rim,no glue required.To this end he had maybe 50 or 60 used rims on the wall of his garage that he would use.I am not sure that this always solved the problem of the air finding that path of least resistance but it did go some way toward it.He also constructed a small compressor from a refrigerator motor to facilitate inflating them.He even replace sections of the inner tube by cutting out a badly blown section and gluing in a section from another damaged tyre.If a tyre can be made by hand in a factory it can be repaired by hand in some ones home, Geoff Duke in Melbourne Australia