Obviously those I've seen I've seen to fix
From memory I think most had done around 100k but the problems were with the LPG system not the engine itself.
I don't remember seeing a lube system fitted on one and have never seen one with a problem associated with VSR. However, I don't know if these models are fitted with tougher valves / if the vehicles I've seen wouldn't have suffered VSR even without a lube or with a vapour injection system. I cannot see how liquid injection could make any difference, especially in case of the exhaust valves. The exhaust valve is hardly going to benefit from any marginally cooler intake charge/fuel intake temp!
The liquid LPG injectors on these models are apparently a very old spec petrol injector that can handle the higher pressure of the liquid LPG (while of course not having any components that are not LPG compatible). Vialle went bust shortly after I fixed the last one I worked on, I've had no call to try to get hold of parts since then.
Full time LPG installer
Servicing / Diagnostics / Repairs to all systems / DIY conversion kits supplied with thorough tech support
2 miles A1, 8 miles M62, http://www.Lpgc.co.uk