1/8 inch piano wire with a brass bushing .
I dont lubricate any of my control connections, it accumulates dust and dirt and wears them out faster.
If you feel you must perhaps some graphite powder would be appropriate

I was wondering if all those fibreboard bellcranks that different people sell just let the axle run through a hole in the fibre?

I have to make a decision today. 

I'm leaning toward gluing the 1/8" rod to the bellcrank and having two 1/8" ID brass tubes above & below, glued to the centre rib.  This would give more bearing area than the reverse.

What Mark said! I think Geoff might have been thinking of gluing the oilite bushings to the bellcrank, which would be fine, too. Are you going to tilt the bellcrank to align better with the flap pushrod, assuming there will be one?
Another good idea...  Steve

This bellcrank is the prototype of a new theory I testing. 
No doubt, this will flush out a report of how somebody did this 55 years ago, so bring it on !!

It's sort of a "Russian X-Crank" with two output arms.  Each output arm will drive ONE flap, thereby eliminating the troublesome torque rod that traditionally joins the two flaps.

Obvious benefits include:
  Dividing the stress between two two push rods and two control horns.
  Independant adjustablity of either/both flaps.
  Balanced forces on the bellcrank.
  Flaps do not tend to lock out if the wing flexes.
  Tolerance of dihedral and/or swept trailing edge.
  Ability to use large nylon horns, securely bolted to flaps, in lieu of Lucky boxes, etc.

This is a "profile only" setup, at least for now.

The output balls are about .40" above/below the CL of the bellcrank, thus giving a head start toward a straight line linkage to the horn.  The geometry can be further squared-up by placing the horns a little forward on the flaps.