Hi Dave:
I was in CMC (Cooper Motor Company) down in Nairobi's Industrial Area a few years back (1999 I think) when the P38 had just come out. The workshop area was full of brand new P38's (Government Ministers!!!) which were all suffering from the same problem. The workshop manager told me they had broken engines due to the high sulphur content of the fuel out there. I don't think oil changes would make a difference here. If you want I can try to get a number to call (CMC's) or somone else who you can talk to about it but don't forget that parts for cars in Kenya are VERY VERY expensive due to import taxes. At least twice as much as parts in the U.K.
My advice - Get yourself an old 2 door 3.5 V8 classic sorted out without anything to go wrong (electronics/suspension etc).
Karibu,
Rich