I built up an S-works tarmac for a customer about a month back. He has quit racing and built the bike to be comfortable. It has a 15* rise stem 120mm length stacked with the fsa cone spacer that cam with the bike and 3 -5mm spacers on top of that.

The customer is complaining that the headset is basically locking up when he starts climbing/ torquing on the bars. It happens when he stands up and stays locked up after he sits down. He says it also happens when going over cattle guards. I have not been able to replicate it at all on 4 seperate rides.
I have taken out the little dust seals at the advice of specialized, but it made no difference. I have also taken out two of the 5 mm spacers (placed them on top of th stem) which looked like it was going to work but didnt.

SO my question is has anyone else seen this? Any suggestions? Will any other brand of headset fit? I asssume so, however my rep at specialized told me not (i rarely believe the tech guys at specialized warranty, not to mention they treat us like crap because we are a small dealer)

Thanks