SAO 58521 Revisited.
Yes; We've been here before! I resumed monitoring 58521 late Autumn. Playing on a hunch, I settled down to watch the star continually for extended periods during recent sessions. 58521 appears to fluctuate between 9.8 and 10.3 magnitude over an irregular cycle of between 1½ to 3 minutes. The fall is rather abrupt; say 20 seconds. 58521 then regains full brightness at a more leasurly pace...and so on. Perhaps someone would care to have a look. We're talking about the orange star at the centre of M37, for anyone new to this.
Stress this requires watching intently. Settle down in a comfortable position. A binoviewer is reccomended and a power of around x150.