Dan,
The change occurred in the April 25, 1985 update:
"Change B1 from 3160-0209 to 3160-0450 FAN-24VDC, 36 CFM"
The closest I could find in today's market is the EBM Papst 8124G. This fan has a specification of:
35 (not 36) CFM
38 dBa
18 - 30 VDC.
I also found this fan in several 5335A counters installed at the factory by HP, so I figure it's the right one. I found some for about $22 in an online search.
The 8124K is the ball-bearing equivalent to the 8124G, which is sleeve bearing.
Hope that helps!
Regards,
Joe
