The luff sleeve is an argument with a sharp object, not a sign of too much UV. The only danger I can think of, is the mast going up the sleeve, if it jams in the cut, it could make it worse. Otherwise I wouldn't bother repairing it, shouldn't get worse from just sailing. The fading could be another matter though, but I'd wait until something happens before bothering about it.

Okay, thanks for the advice decrepit and LeeD, appreciate it.

Dacron sail repair tape will adhere nicely and keep it tidy and the edges from unraveling. Your probably can find it in a matching color. A lot of times, we get freaked out about holes in the luff sleeve and forget about the big hole called a boom cut-out. As long as you can keep the hole from getting bigger, you'll be good. As others have said, just take care when pushing the mast in. It may be better to work it up slowly from the middle rather than jamming it up from the bottom.

Pro tip: round/radius the corners of the tape before you peel the backing. It makes it less likely to pull/peel up later. Same works for clear tape, too.

Give the stray threads a trim with scissors, then run a lighter over it, ( lit obviously ) just to stop the threads from fraying any more, then stick a bit of Dacron sticky back over it, job done.