years ago there was a lot of discussion on using oils for fuel in these engines.
i think the general consensus came down to the following
1. yes these engines will burn just about anything flammable
2. raw vegetable oils over time seem to gum up piston rings, so expect to do more maintenance or repairs.
3. raw vegetable oils (used) can have a higher acid content which is hard on injection components, particularly pumps,
4. motor oils can have a high ash content, which when burned make a fairly good lapping compound and over time accelerate ring and cylinder wear. modern low ash oils should be less of a problem, but the problem seems to be real and persistent.
having stated these, i will add my personal take
1. if you are using a museum quality lister that you deeply care about, and don't like to or want to have to do more frequent overhauls, i would recommend not using raw vegetable oils (new or used) or used motor oils.
2. if on the other hand you have a listeroid, or a changfa type engine, don't mind having to do more frequent heavy maintenance/overhauls, and have a ready source of cheap parts such as cylinder kits (pistons, rings, cylinder sleeves) and have done the math as i have you might well conclude that the savings on the cost of fuel vs the added costs of operation (labor/parts for overhauls) favors the use of these fuels, then i would recommend you burning these types of fuels.
as i see it there are two very different camps when it comes to these engines, and i agree with the positions of each for different reasons.
there are those that have antique engines that are bone stock examples of the engine type that should be preserved and protected for future generations to enjoy the operation of. so if you have such an engine it should be protected with good maintenance, shorter run times and burn only pump fuels of known good quality.
there are also those that have either older repaired examples of the original or the various copy engines that are expected to work on a regular basis and as such the cost of operation is of primary concern. these owners might well have done the analysis as i have and concluded that parts like cylinder kits are to be considered as "consumables" no different than a paper element air cleaner, having a finite lifespan where one expects to have to replace these parts on a determined basis.
both positions are valid, you just have to do the analysis and determine which camp you are in.
fwiw
bob g