I believe you are referring to "Stoddard solvent"...Britspeak for mineral spirits. It's still available, though it's not quite the same as it used to was.
It does cost about 10X what it did when this board began. It's still the best general-use cleaner, for most parts.
For airfilter foam, mineral spirits is about the only solvent that won't chemically melt the polymer. My point being that MS is a good first-stage cleaner; it has to be followed by subsequent stages of cleaning. For an air filter element, that's a water-soluble detergent. It could be actual laundry detergent, Simple Green, dish soap, TSP, etc. Think about it, foam filter elements are oiled...petroleum based chemicals are fine.
Following mineral spirits, for engine and hard parts cleaning, brake parts cleaner is about as good as it gets, for final-stage cleaning. You don't want to go crazy with the stuff; it's expensive and not exactly safe-as-milk. Once steel parts have been cleaned with a "hot" solvent like this, they'll flash rust, unless oiled.
Lacquer thinner has all but vanished. What's sold as "lacquer thinner" is labeled "gun cleaner" or "Spray gun wash", etc. It's nearly as effective as brake parts cleaner. There's very little actual lacquer thinner in the mix anymore. Read the label, you'll see what I mean. Try not to get a migraine.
Acetone and MEK are highly effective. Both are nasty to work with, especially MEK...I avoid that.
Paint prep cleaning solvents are a topic of their own.
