coolant remnants by cap

I’ve started loosing coolant slowly for a few months now. At first I didn’t want to worry about it but now its becoming tiresome.
The coolant level drops a bit during the week causing overheating at stops/idling. The only thing I’ve seen so far is a bunch of powdery rust around the cap. Like the cap is leaking and the fluid is burning off around it.
I replaced the thermo about a month ago since my upper hose looked a bit bloated. Like the thermo wasn’t opening and the hose was expanding from back pressure. Don’t know if that’s right or not.
Anyway, should I just replace the cap? I replaced it for the hell of it last year. GOt if from Autozone.
Also, I want to run a flush but my radiator drain plug seems to be so close to the crossmember below it that I can’t turn the plug to get it off. Weird.