I think very highly of Sikaflex 291. I used to keep a tube of it in my Boler
and garage to use on almost anything. I used it for re-bedding windows
, vents, fixtures and sealing around things I didn't really want to take off and re-bed when I reno'd. A dab under every everything and I haven't had a leak in a year (except through the worn seals of my jalousies that is...).
I don't recall having used it on any holes though...I would if I HAD to though...Like, for example, if my Boler
was in space and the only thing that kept me from getting sucked out into the vacuum of space through an 1/8" hole was to fill that hole with caulking rather than wait to get home, spend 5 minutes with some epoxy and a popsicle stick.
Anyways...Sikaflex 291 adheres very well and has lasted 3-4 years (and running) in places where I meant it as a quick-fix. Tip: It cleans up before cured very well with wet-wipes! It is much easier to clean up once cured than sil-ick-cone.
For holes that you want to fill, but don't want to hassle with epoxy I really like Francesca's idea (...the first one, that is! ;D ). I will probably use that in the future if I accumulate excessive holes in my Boler
for whatever reason. One could even use sikaflex to caulk the little plug in place if you feel absolutely inclined to use a caulking gun.