The reason for this is well known and covered elsewhere. One VCO was not locking - easy to find which one it is but why....??
All DC Voltages were OK so probably not transistor/bias. Must be the conductive goo syndrome or a faulty capacitor/coil.
Once the RF board is out of the radio how do you tell?
No power on the board anymore so no way to run the oscillator to find out if it's off freq or just won't start.
I decided to compare with a GDO the dips I got with the faulty VCO and it's neighbours next door - about 5MHz higher/lower in freq.
It turned out when measuring the main tuned circuits I could see a good dip on them but on the this VCO's transistor base dip was flat/absent. On neighbour VCOs dip was still visible although not very deep.
I changed (one at a time) capacitors around the tuned circuit. On replacing 47pF capacitor in series with VCO tuning diode dip returned with same depth as all the others. Board was put back in radio and now all FB!
Suggest using GDO to check oscillator tuned circuit Qs when board is out of the radio and can't be powered up.