Trouble gluing cap on hot water faucet
Try Araldite or Milliput - both are different types of epoxy, araldite is a two-part paste, milliput is a putty, and the latter is recommended for repairing radiators, so should be plenty heat resistant. The downside to milliput is that it is not especially sticky and also has bulk, so you might struggle to make a thin, solid join. Araldite should have no such issues, but I can't vouch for its heat resistance.

edit: I have just read the remark about having to reach the screw - in which case be wary of Araldite as I have heard of plenty of references to it needing something akin to a small bomb to shift it once it's cured. If you go for this, use a tiny dot that you can easily crack with a little leverage.