1942 BSA- A little off topic

[Brit plumber]

It's the forty odd years since they were released from the Army that causes the build up. As far as I know it's true about the OMD not being much good for your own engine unless you know it to be clean. From what I understand, civilian oils were often based on vegetable fats which broke down and built up in the sludge trap, if you then put OMD in the engine it could move the sludge and block the oil galleries and the quill to the big end with dire results. Like you say, how much of this is a scare tactic to prevent people from pilfering military engine oil I don't know. I've always stripped my crank cases down, I find it therapeutic to strip a dirty engine down, clean it, replace parts as required and rebuild it and then wonder where the extra nuts should go. Thank god for digital cameras, they got me out of a few rebuild messes!