What's wrong with the Lucas pump for veg oil?

[swagamuffin]

As of yet I haven't got a definitive answer for the above question. Some say it's the seals, some say its the mechanism (plunging not rotating iirc), some say it's the viscosity of the veg oil, others the vanes in the pump are weak. It could be all of them, but if it's just the seals or the vanes surely they can be uprated? There are stories of Lucas pumps getting a good few miles on veg.

[thatdude]

Can you "thin out" the veg oil with e.g. diethyl ether or something?