Conventional diesel for 100K+ miles and fuel filter(s) changes about every third oil change.
Page two, post 21 of this thread shows a 'side by side' photo of the nozzle and spacer described and a ~50-60K mile WVO nozzle and spacer. The WVO nozzle was FAR beyond worn out. Also, the other close up photos of the WVO injector parts. [brief description] The honey colored goo coming out of the fuel feed hole was the consistency of honey or pancake syrup AFTER an two hours in a hot ultrasonic cleaner. The spacer disc appears to have small bubbles on it. These were hard and gritty but much easier to clean. Gentlemen, you have the photographic "proof" of polymerization of WVO in a fuel system.
My personal opinion is
IF you use WVO, use it as stock to make bio diesel and clean it meticulously. If you use diesel fuel, get it at a busy truck stop, use your own cans and filter it before putting it in your tank, when possible.