make sure the allen is seated-

I'd hit my allen socket with a hammer(assuming it is clean). Hiting it quite hard will help break the set. Not a continuious beating of frustration- just one solid hit of "judicious force". You need to make sure your not twisting it out. You need to hold the racket at the pivot and at the handle. I've always heard pucking the socket up with valve grinding compound helps.
Use a high-quality allen socket. Absolute best would be to use a stahlwille.

And make sure you use new ones when reassembling!
If you strip a 6 point allen, you can ussually beat a 12 pointed star into it for removal.

Michael

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Michael McGuire
83 300d
01 vw A4 TDI
66 Chevy Corsa
68 GMC V6 w/oD
86 300E