Alan wrote:

(1) to avoid the oil dripping off the blades soon
(2) to have enough lubricant powert os top wear
(3) to avoid holding paper dust such that over time it becomes congealed.

Number 3 is pretty important. The combination of
lubricant and paper dust is very abrasive to
machinery. This was a big problem during the
days of punched cards.

Note the difference between grease and oil.
Generally speaking, places that need grease
should never be oiled and places that need
oil should never be greased. Grease acts
like a solvent for oil.

Rather than trying to re-engineer the lubrication
system, I'd stick as closely to the manufacturer's
design as possible, because there might have been
engineering considerations you're not aware of.
For example, what if the machine catches fire?
A PTFE-based lubricant would emit toxic gases.
A silicone oil might spread into the motor or
switch contact points, causing an open circuit.
If a light machine oil is the closest substitute,
that seems like a safe bet. My mom uses 3-in-1
oil on her sewing machine. I don't know if that
brand is available in the UK, but from your
description of the problem, that seems like
a good fit.