Does anyone know how to realign the prism in a LaserDisc player?

Hello! I’ve got an old Philips VP831 LaserDisc player that I’m trying to fix. When I first got it, the disc would spin up then the objective lens would clonk up and down a few times then the disc would spin down again.

I found that the glue in the prism had gone cloudy so I bought a new prism to put in it and installed it. I have my oscilloscope set up so it’s monitoring the FD signal (the one where the outputs of the four photodiodes are summed) as well as the focus error signal (where an elliptical shape of light is detected when focus is wrong).

I’ve been fiddling with the prism adjusting it tiny bits at a time for hours and I can’t for life of me get it aligned well enough for the focus to lock. I know the focus lock circuit works because I can pull the FD signal low and the objective stops clonking up and down. I know the FD signal is working as I’ve occasionally had it so that with the focus lock sensitivity cranked up the objective almost stops but the FD isn’t held low long enough for it to lock.

Is there any way I can get the prism aligned properly without specialist equipment or am I screwed? I haven’t touched any other optical adjustments at all so I feel it might be possible. I would love to get this working so I’d appreciate advice from any LaserDisc gurus out there!