Any idea where I can get a propane regulator for a '93 Marquis 6500 LPG generator.
Is your regulator inside the generator or external? I have seen both on that model Onan.
And is yours liquid LP or vapor (look at your propane tank to see whether the generator line comes off the liquid or vapor port).
Internal
Liquid feed
Pull the old regulator to verify, but very likely it is a very common IMPCO model J regulator.
No reason to replace vs rebuild. Not difficult to rebuild, but if you have any concern, have any propane shop that works on propane powered vehicles, fork lift's etc do it.
You will need to pull the generator out to access the regulator.
IMPCO RK-J Repair Kit For Model J Converters: Forklifts: Amazon.com:... (http://www.amazon.com/IMPCO-RK-J-Repair-Model-Converters/dp/B009SEJ0W8)
RK-J-2 Repair Kit for sale | eBay (http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313.TR0.TRC0.H0.TRS5&_nkw=RK-J-2+Repair+Kit&_sacat=0)
And, as I have mentioned before, a VERY good idea to convert to high pressure VAPOR. When you open the regulator, check for a light viscosity grease contaminant-- the result of using liquid in a regulator "laying on its side".