Yes, you can replace the thermal....BUT, it must be JUNO's.
Yes, there is a 30PAR20 lamp (WW Grainger Catalog)
The fixtures are 'cycling' due to the thermal OL; be it old age, wrong lamps for to long, or poor ventilation, or a combo of the above reasons.
Also, bulb (30) is physically larger than 20, and PAR bulbs reflect heat back, as opposed to "R" lamps. The PAR heat is the 'root' of the problem