727 reverse failing.

Hi out there.
I have a 1964 727 Torqueflite auto box which has just started to lose reverse gear (almost completely gone).It had being standing for many years. I have filled and drained it a couple of times before running under load. I'm just a regular guy so no heavy technical answers please. I have looked at other threads on this subject and have seen many different answers. None of them has mentioned something that I have noticed in my situation which is coupled with the reverse going. The oil level in the dip stick/filler tube is very high up inside. 3" above full mark. Way way higher than it should be. Could this be an indication as to whats going on. If I was to guess I'd say I have a blockage stopping the oil from recirculating back into the system therefore backing up. But it may well be something more onerous. Any help would be appreciated. Thanks.