we did at one time use boiled linseed oil for building cast iron boilers, the type where you bolt together any number of "sections" like a sliced loaf of bread to achieve a given output of heat, I am talking about really big things, tall enough so that you can stand up inside, the sections are joined using a tapered nipple that allows the boiler to grow and shrink with heat/cold cycles, and the linseed oil on the nipples was a brilliant seal, as long as you cleaned up the ground surfaces with a spirit before hand, you can also find it in the threads of the bonnet on almost any brass gate valve, no gasket juts oil on the threads, and capable of withstanding very high pressures and temperatures.
CLEM