I have no experience with the Winchester, so can't help much.

But I can answer one question. No, there's no such thing as too clean with a muzzle loader. However, there is such a thing as too oily. But even with an over oiled gun any firing problems should only occur with the first shot. The first boom should burn up any residual oil and following shots should be OK.

Are you swabbing between shots? If so, describe your procedure. We may spot something that's causing your problem. Have you noticed any pattern to the problem. For example, does it usually go bang with the first shot and fail on the second or third? Are you using bore butter by any chance? Have you taken a close look at the flash channel and flash hole to see if there's carbon build up reducing their diameter?