one of the points I've seen Doghead raise on WMO being used, and the effects thereof: Waste motor oil is not listed as an acceptable alternative fuel.
Also, the multifuel engine was designed with a bit different purpose than a toyota sedan engine, they're not going to go 400k miles with minimal maintenance. I've seen new guys advised to stock up on as many spare parts as possible; that advice has to have good reason behind it.
That being said, I run WMO, and pay taxes on the amount that I use. The only issues that I could possibly, recklessly blame on WMO for engine component breakdown would maybe be an o-ring on my manifold heater, the O-ring was made out of Buna-N, which is described as having less-than-desirable tolerances to alternative fuels (such as brake fluid, gasoline, etc). The failure of the o-ring on the end of the injector caused oil to jettison onto the top of the turbo. O-ring replaced by Kelrez type O-ring. Now my heater has an O-ring that wasn't made by the lowest bidder.
To determine which O-rings can tolerate which environments:
O-Ring Material Selection / Comparison Guide