Spoke to several different people today about this issue, some mechanics that convert cars to LPG running and also a couple of people from Ford. None of them were able to tell me whether or not the ST170 has hardened valves seats (and can thereby run on LPG).

The gas people all recommended flashlube and advised against replacing the valve seats because of expenses, they were talking ~€ 1500.

I don't see the point in installing a flashlube system if you don't know for sure you're going to need it.

Still need to know more about this car before i can actually decide to buy it.
If the flashlube thing is the only option i might have to look for a different model.

Investigation will continue tomorrow.