Yeah, the drift could be Doppler, that definately would explain it. Interestingly there was not a pass over or near over my location at the time, so I had to be getting it via good old HF propagation. I had not listened for this beacon for years (since the last time I worked it Mode A right after launch) and forgot all about it. The last time I heard it the sag was not as pronounced as now.
T!