Service manual

On the coarse feed - advance/retract?

Yes   The the gear engages and then jump left when looking from rear of the machine. Like there is something missing  on the other side of the block. Washer or o ring???

I"ve never seen that issue - something must be loose and/or worn in that mechanism. Unfortunately, the service manual doesn't give that much detail. As I recall, the two bevel gears are brass, and so is the large (54 tooth) ring gear. I assume that the plastic gear, of which you speak, is the one underneath the large ring gear (which engages with it). That gear (item #5.10) doesn't have a part number listed in the service manual.
Is it only the plastic gear that jumps? Since I don't have one in front of me, and the service manual doesn't show it, I can only speculate - perhaps there is supposed to be a circlip or something to hold the plastic gear to the bevel gear. Can you get a mirror back there to take a look?

Thank you for your help. I called Thermo Fisher and they saying there is nothing missing. They wanted to come out and fix it. Ofcourse. Customer is ok with that. I just think there is press fitt and is stretched. Case is closed for me. If you text me cell number i like to send you 10 sec. Video for you to see and future repairs.

again thank you. 618 641 3404

Stanley