This video just popped up.  Interesting results.

 

Acid for the win. I wonder if it causes any issues with the aluminum pistons?

I would be a bit scared to do that.. (use vinegar on aluminium..)  I got a old L24 that needs some restore work but i prefer to just use some WD40 and let that first soak for a week or so.. (I'm in no hurry, hurry is wrong with these kind of things!)

somewhere I recall soaking pistons in antifreeze (great stuff) in a crock pot for a day would get them super clean. 

Evaporust FTW. It does not remove material like acid would.

I've always had good results on aluminum and most other metal with lacquer thinner. 6 Z pistons fit perfect in the bottom of a five gallon bucket. Cover with the thinner and put a lid on, it evaporates pretty quick and stinks too, after a few days I blow them off with my air compressor. They look like new.

A few years ago it was $9.99 a gallon at Lowe's, now it's $25.