Blower/airflow sensor needed for BA32

The BA32 is the baby VAX BI chassis used in the 8200/8250/8300/8350 systems - I have an 8250 (it'd be an 8350 if I could find another CPU :-) that has some problem with the cooling. The blower speed seems to vary all the time it's running, and it's constantly speeding up and slowing down. The system wil run for about an hour and then trips itself off, presumably either because of airflow or overtemp. Can anybody tell me if the blower speed is supposed to vary like that? Does anybody have any maintenance prints for the BA32 blower control? Anybody got any spare parts they're willing to sell? I spent a long time putting it back together after it'd been stripped by a scrap yard, and I've actually got it to the point where it will boot VMS now, so I'd really like to fix this last problem. Besides, it's a really cute little system - I believe it's the smallest VAX BI box around. Thanks, Bob Armstrong