I have been having an intermitent problem with my brake pedal.  When I press on it the brakes work fine but sometimes  it is slow to return to its normal resting position.  The problem seems to be related to hot days so far as it only happend when it is above 30C or 86F.  Other than that the brakes work fine.  Could this be related to a vaccum leak somewhere?  I can help it along by pulling the pedal back up with my foot.
 
Thanks.
 
Pascal
'84 Westy