Shimano Chronarch 100A cast control cap

New member and new to shimano b/pc's.  Awhile I go i was given a Chronarch 100 a with a trolling rod. Being a rookie I lost the cast control cap. Searched internet with fine toothed comb trying to find the right cap. All of the sites I found said they were pretty much obsolete and discontinued. So I bought one for a SF or MG. has a bronze finish but doesn't really thread on properly I feel. It starts to but doesn't go far enough to apply any tension or cover the O ring. I guess I'm asking if anyone knows of a interchangeable cap or if you have an extra lying around will you sell it? If i find one that works I will ve sending the reel in to be cleaned and serviced, if not it will be put away.