You don't give a location, but in some big towns there are old specialist companies that might know more than the generalists like NAPA (which, however, certainly is more likely to be of help than the chains that mostly sell oil filters, batteries, and such). For example, here in Seattle we have an old outfit, Brake and Clutch Supply, that has been around for ages and is likely to have an old-timer on hand that remembers everything. Also, companies of this type always sell better parts than the chains.