[Test-Equipment] HP 8640B Filter Cam Woes

[Barry]

Upon opening the housing (where the cams are that drive the filter switches), I discovered the cog that provides the positive click/ratchet/stop function is broken.  It appears that this part, along with the cams themselves, are made of a material that shrinks like the infamous Delrin gears (the cams may be Delrin too) and that's what may have contributed to the cog's failure.  Looking carefully at the cams themselves, they, too, appear to have stress cracks possibly from shrinkage although these are not very bad.

I think I can repair the cog such that it can't break that way again by reinforcing the shoulders with a metal sleeve; however, since it was broken when I got it, I'm unsure of the orientation of the stop arm with respect to the flat on the shaft.  The cog and cams have "D" holes and the shaft drives the cog with its flat but, depending on which way the cog is placed on the shaft, the stop arm's position is correct in only one of those ways.

I notice there's a dot embossed on one side of the stop arm and a similar dot on the face of the first cam (cam "A").  Are those indicators?  Should they face each other, away from each other, or do those really indicate anything about the cog's orientation?

Yeah, I know it's a long shot and most likely won't get a definitive answer, but thought I'd put this out there just in case.

BTW, here's a picture of the cog/cams assembly I'm referring to:

http://www.qservice.tv/vpasp/shopexd.asp?id=3063&bc=no

Thanks,
Barry - N4BUQ