634 synthetic separates almost instantly from the water. Floats on top of the water in the tank. Fill the tank before it gets two low and you will never get it into the pumps and boiler.
I did not run the car all that much before I changed over to the Derr boiler maybe one or two short tours, the original boiler had many tubes plugs, it was an original welded steel tube boiler. I canít say weather the water mileage improved or not but the condenser was very clean.
I still use 634 in my 1906 EX with no problem. When I first started running my EX I went back to Steam cylinder oil as I had 10 Gal on hand, but the pump and small 3/16 oil line gave me a lot of trouble. I broke a valve rod on my first tour. No oil. I switched back to the 634 and have had no problems since. Ití pumps through the lines a lot easer.
Recovering the oil I never tried.
If your running a condensing car it will never get oil into the boiler. I donít think you will notice any difference other then a clean condenser and boiler. The only problem is you canít see it in the winker. Brent Campbell started using it and added a die to darken it so it showed up in the winker. My 1906 EX has no winker, I never added one. I think the first one came out in 08. [www.stanleysteamers.com