Update - it finally gave up completely a few months ago and would not stay on regardless of what I tried. With nothing to lose, and knowing they don’t fare well in this sort of environment, I decided to replace all the electrolytics. It has worked perfectly for the last ~4 months. So, for a few bucks worth of parts, problem solved - at least for now.
If you’re handy with a soldering iron, here is what is required:
1 x 47uF @ 50V (C11)
3 x 0.47uF @ 50V (C4, C7, C15)
2 x 1000uF @ 35V (C16, C17)
All radial electrolytics
Hope this helps someone.