These are pictures of the one of the heads of my 3.0 1998 MV6 with 130K on the clock.

In the last 40K or so miles I have done...
It has mainly been run on ordinary Shell Petrol.
Very occasional fill-ups of supermarket fuel (but normally the higher octane variety)
Occasional High Octane Shell

Roughly 3 times a year, a fuel cleaner, normally Forte Advanced Formula Gas Treatment  was added. (Before I found Forte, I used STP or Redex Injector cleaner)

Heads had to come off due to Head Gasket failure & Coolant loss....









Here is a typical picture of a 2.6 head after 100K miles:



and the valves (note the state of the inlet vales in particular!)