I could use some advice on this as well. I bought my son a 2019 KX 100 last Xmas, and like an idiot I bought it from a race family with only the Manufacturer certificate of origin thinking I would just have to the DMV for a vin verification. I loaded up the bike and took it to DMV, went inside paid my fees etc. and then was told to drive around the back of the building for the vin check. Vin checked fine but the engine was missing the Motor ID number so they would not complete the paperwork. I reached out to the guy I bought it from and of course he had gotten from another race family that swapped the case out when they built the motor and factory replacement cases do not have motor ID numbers. Anyhow I went home angry and have not done anything with it since but want to get it registered prior to desert season.
Has anybody successfully stamped a motor case themselves? I really don't know what else to do unless I try the CHP and see if they buy the story and somehow will sign the paperwork. If not, I am going to have to try and sell it hoping another race family buys it and doesn't care.