If you can rebuild a gas carb you can rebuild a regulator. The main thing is to be careful with diaphragms and gaskets to prevent leaks. If you find a lot of greasy residue inside it can be oils that settle out of the propane as it vaporizes or it can be valve grease from the cracking plant put there by an over-zealous workman. The suggestion to keep the coolant temp low in the vaporizer is a good one. If you can, orient the regulator with the vapor outlet down so that the residue tends to go through the engine. It's just more hydrocarbons and the amount is generally slight if it isn't allowed to build up. One symptom that turns up in dual fuel apps is that the engine won't start on propane, only on gasoline, then can be switched over when warm. That's almost a sure sign you have gunk in the regulator. It solidifies when cool and liquifies at higher temps. Good luck.
Keith