I would agree about not using a plastic type tank liner on a oil tank (bag) as many people experience adhesion issues. However small leaks are easily corrected. I am a big fan of high tech welding, and while I am only at best a marginally skilled welder, I worked with some of the best welders in the US and still access many of them who are willing to do small jobs on the side. Cannot beat a skilled TIG welder using the best materials. And fabbing a new tank, thats what I would do.
But repairing a vintage and well worn & seasoned,,,,,,,and by seasoned I mean metal fatigue. I would braze it. Some oil tanks are either silver soldered or brazed in initial construction as well so, examine joints, fittings and seams carefully. But good old school brazing on a properly cleaned surface will do the job just fine. Follow it with a leak test. (Warm the tank to oil operating temps and then add water or petrol and look for a leak, (Be careful that the liquid is also near same temp) I would avoid pressure testing.. If still signs of a leak easy to clean and prep again.
Silver solder is also a viable method but less common. Olden days some metal workers and body shops used lead, but not a easy skill to learn and not suitable for joints and sealing surfaces.
As to all these drastic chemicals, thats a bit over kill. Find a radiator shop or commercial stripping shop and have the oil bag dipped. I use a commercial shop down in the city industrial district and oil bags are $20 each to have chemically stripped. If you want to clean and strip it yourself,, paint stripper and then clean with MEK or just use plain old Lacquer thinner from a body shop supply store. (Lacquer thinner is not used anymore for paint but still sold for cleaning parts or cleaning paint equipment). If you want the next level of chemical clean then buy some brake cleaner solvent in a aerosol can. It will clean the last remnants of oils away and drys quicky with no residue. (Did somebody say "Earth day"???)
Trichlor is an awesome solvent and lubricant. But highly cancer causing and very dangerous. I used to LOVE using it for a cutting lube. When cutting or grinding on stainless or high grade steels when used a cutting lube the carbide tooling slices thru and removes metal like its butter.
This is because of its unique properties. Skin, when exposed to it will get frostbite. There was a few very stupid employees I used to work with, who huffed it. Squirted it inside a container and used it as an inhalant. I bet they are all dead now,., they were pretty low functioning to begin with. Ironically, one was employee of the year because he had perfect attendance in 10 years of employment.
