You're the 2nd one to comment about the leaded gas causing sludge, so there must be something to it. I always heard it was Quaker State or Pennzoil motor oil. Learned something new today! :)
Actually, it was not leaded gas. People say that because it kinda all fell together "about" the same time as lead's exit. Here is what happened.....and the only reason I know is because I was in retail auto parts sales in the late 70s and very early 80s as a kid and got in on some really good oil seminars.
"About" 1977 "or so" several million barrels of a few Penn brand oils got a bacteria set up in them that the refining process normally removes. This bacteria causes sludging of the engine oil. I just so "happened" that Quaker State Oil was the main oil brand that got "most" of that bacteria. It like to have killed that brand. There is nothing nor was there ever anything wrong with the Quaker State brand. It was refining process that failed them. To this day, lots of people remember Quaker State for that problem, even though the brand had nothing to do with it.
