A few things regarding the Canyon. The steamers threw oil everywhere where as the diesels did not (sealed roller bearings on alco's and well sealed bath lube on f40's), crater is another story. However, for the last two years they ran steam they were using biodegradable animal fat based bio-oils for everything but the cylinder oil. The cylinder oil (though petroleum based) renders itself well to hydrocarbons decomposing in the sun light VERY quickly as it comes out atomized. That is it is broken down into VERY small particles that the sun will quickly attack.
The "conversion" to burn veg should not be that extensive. In fact, all they HAVE to do is clean out the tank, fuel lines and replace every bronze component. See, the bronze does a pretty good job of absorbing the petroleum fuel oil(very porous), once WVO starts flowing past it a "film" begins to grow and continues to build and will cause problems. If they are wise they will put something better than a drooler burner in the thing. The burners referred to in the trains article a few years ago actually burned more fuel than a drooler regardless of the propaganda that stated otherwise.
The work the locomotive is getting is likely more that of fixing the issues resulting from an improper conversion to oil lubrication on the main journals. Bronze other than that speced for crown brasses and a failure to line the brass with tin as is required on high speed high axle loading locomotives. For comparison, Flagg Coal could use straight crown brass bronze with now tin as it is slow and lite.
The 4960 had almost 1/4 million dollars put into it in the course of the "oil conversion" on the journals. It failed repeatedly, first because militec was added to the bio-oil which broke down the animal fats and rendered the oil useless. Then, the failures continued, ultimately Xanterra was told it was going to be over $125,000 to make the 4960 right again. I don't know if they have a proper repair plan at this point or not but I would put money on the idea that these are the issues they are dealing with more so than anything that needs to be done to make the engine burn WVO.
You want to know why Xanterra (yes xanterra not the current owner, steam was killed 3+ months before the sale took place) killed steam? Read the previous paragraph, the steam side of the railroad began deteriorating mechanically from the time Robert Franzen left.