At work we had Linde forklifts with vw 2.0 engines fueled by propane. They just got replaced, not for engine issues necessarily, just generally worn out. Here is one of the old ones waiting to be shipped out.
<img src="http://www.tractorbynet.com/forums/files/buying-pricing-comparisons/411002-any-news-gas-engine-cuts-forumrunner_20150210_235122-png"/>
We run 5-6 days per week, 3 shifts. Look, this one is nearly new... I think the life of these engines is quite disappointing
<img src="http://www.tractorbynet.com/forums/files/buying-pricing-comparisons/411003-any-news-gas-engine-cuts-forumrunner_20150210_235151-png"/>
I know it was mentioned before but maybe propane would make a good alternative.