HeathKit GR-21 FM table radio schematic of manual

I found a Heathkit GR-21 FM table radio while out looking for albums.
Seems as if it has original tubes, and works, except the tuner seems to jump around, A few minutes after tuning in a station, it disappears. When I retune it in, it is at a different frequency. However, if I tap on the tuner, the station comes back in (reminds me of when I was a pre-teenager, and had a tube table radio that did the same thing). This unit has AFC, which has to be shut off while tuning in a station, then engaged.
Anyone got a schematic for this unit? I tried BAMA, but no luck. I figure that in the process of tracking down where the problem is, I'll learn a lot more about receivers.
Best Wishes
Bob, W7ETA
"AC volts and DC volts and little lamps and lities..."
Here is a link which sells the manual for $7.
Never heard of them before. Found by googling "heathkit GR21".