My question involves vehicle registration or title in the state of: California

Here is my problem:
I sold a VW to X in April 2008. A month ago I get a call from Y saying he bought the car from X. Y tells me that there was a problem in the title however, and he has not been able to put the car in his name. Y tells me he can't find X to see if X can fix the problem. Y asked me to sign a document declaring that I sold him the car in June 2008 in order to fix the title. I have told him I will NOT sign this document (under penalty of perjury) because I did not sell him the car, I sold X the car. I'm not going to potentially get myself in trouble over this....
What I believe happened is that X never registered the car into his name, and never signed the title. Instead he just gave the pink slip I gave him to Y when he sold Y the car.
I want to help Y get the title sorted out, and I want to be OUT of the situation, however, I'm not willing to fabricate what happened to do that either. The DMV has not been helpful, as they are the people who told Y just to have me sign a new bill of sale saying I sold him the car, when this is NOT what happened.
I have no idea how to get this sorted out.