I've recently acquired a Marantz VP-15S1 with the custom made anamorphic lens with sled.
I've taken a few photos because it doesn't seem to be a prism based lens as many had led me on to believe reading older posts. It seems to be some sort of small cylindrical lens set to perform the stretch.
Some up close shots of what's inside the enclosure:
There has been some confusion about this lens. I believe it is a hybrid prism/cylindrical (maybe even some spherical elements). I have seen this unit and it seems to not have any adjustments so whilst it might have astigmatism ground in, does not offer (AFAIK) any further adjustments.
There is a focus screw for slight adjustment. Compared to the Schneider Optics lens I had the focus is VERY limited in comparison though. The image shows only a VERY small loss of sharpness which is only visiable up close within a foot. I suppose this has a lot to do with the fact it was custom designed to work specifically with the three Marantz VP 1080p projectors. Performance, based on memory, is about as good as the Schneider Cine Digitar 1.33x lens I had. I'll have to do some testing with some other projectors to see if this performance translates elsewhere.
IIRC that was a "cheap" plastic lens made by Minolta specifically for Marantz. Again, IIRC, Dan Miller of Marantz said that it was their attempt to have their own lens vs. buying the ISCO or Panamorph (it was made specifically for Marantz by Minolta). Can you confirm that it has plastic optics?