Do you not have the correct-sized allen wrench (aka: Hex Key), or did the hole's "octagonal" corners round-out on you? Is it ~really~ an Allen, or maybe a square head? I've had a couple of those. Either way, if it's stripped and worthless, Commander Wallace's tap suggestion would still work, and you might not even need to drill it, if you can find a small set. My experiences with "EZ-Outs" though, has been more along the lines of "EZ-Curse", and I've made-up new swear words as I go... I usually break the easy out, and those things, you can NOT drill out...
Not to scare you, but you might then have to go purchase a whole new faucet just to get the "leak" changed-out... and if you're like me, you'll not be able to get the old faucet off the sink, without taking the sink off the counter... which the wife will then go "Oh... well... in that case, let's buy a new sink." Then you'll have trouble with the drain, and next thing you know, you'll be getting yourself a new garbage disposal!...
A quick repair with $3 US for parts initially, turned into a $350 "fix-it nightmare"... I should have recorded it and posted on ToobYu, and it would have gone viral...
