Hallo Joe
The most problematic items on a gas machine is the gas regulators.I would suggest that you replace the regulator kits every 2000 Hrs even if they are still working fine.Genneraly gas machines dont give much trouble and the engine combustion is much cleaner then the standard gasoline engines.The mechanical function wear EG the mast etc wear stays the same as on standard diesel powered machines.Depending on the environment where the machine is going to work and the service intervals the standard life span of a machine is about 12000 machine hours before it will need a major rebuilt.
I hope this was of some help