Is rack still binding a little or not? It has to move easily I would think. One thought I had was if WVO was used as fuel in the engine and the base oil was polyermised. Not being changed enough because of the product going past the rings.

Over a long term siting situation it could have gummed up the rack. Plus might have impacted other things. I might soak both the portions of the injection pump in laquer thinner as it would dissolve any gum. WVO products and by products turn into a strong glue with time. I was thinking the govenor might need the cleaning as well.

Eight years ago was probably when the use of wvo peaked. You know people put almost anything in the fuel tank then and though things would be fine. A used pump cheap enough can also be found if the need became obvious.

Also check the valve clearances because back then many people never bothered.