I have now stripped & rebuilt the Daisy as follows:

Firstly fully de-greased & cleaned all the internal components, including the cylinder & barrel.
Replaced all 4 "O" rings (Piston head, Cylinder, Valve & Breech Bolt.) Made a new Felt ring in place of the old sponge that fits in the middle groove of the piston head, and acts as a cylinder oiller. (This is a far better option as it is able to retain oil more efficiently). Then finally re-assmbled all the components with a light coating of Browning Ligier shotgun oil.
Set the piston head clearance to provide 1" (2.5cm) gap between the end of the priming-lever & the pistol body when there is no air pressure (as recommended by member TCooper) this is the maximum adjustment possible without the piston head contacting the transfer port face.

After again measuring ten rounds, using Eley Wasp's @ 7.34 grain's my results are as follows:

ft.lbs Min.2.47 Max.2.62 Average.2.50
fps Min.391 Max.402 Average.393

This compares favorably with the information supplied by TCooper 23/6/04. Thanks Again Todd !!

I feel that this represents the most power these pistols can be realistically expectd to produce, and with the complete cost of the rebuild only being £3 for the "O"Rings from a local bearing stockist it has proved to be a remarkably economical rebuild.
A.T.B
John.