Yep, those allens always fill with crap that wont allow getting a decent grip on the wrench that reaches all the way into the allen head....... cleaning out the allens with degreaser and high pressure garden hose, or better yet compressed air, is critically important preliminary thing to do.

Luckily the design of allen bolts generally allow vise-grip teeth to bite into the cap...... Otherwise carefully torch the bolts with propane flame - this might loosen em up.

Basically you're screwed and should probably lick your wounds, reassemble and abandon the operation until you've got fresh replacement allen bolts on hand.