Two parts to this:
1. Is it worth replacing the rubber oil seals visible on the drive shaft and on the propeller shaft? I assume the real sealing is done in between the bush and shafts of these in which case how important are these seals? If I have it all apart (which I nearly do - see below) then so long as they are available I will replace. But
2. Can anyone advise on how to dismantle the gearbox drive shaft on the 40 plus. I believe the screw headed bolts that hold the gearbox cover on act as a retaining screw for the bush, this has been removed. I have tried pulling it from the square drive shaft whilst applying moderate heat but nothing budged. I also tried tapping the gear itself protected with a trusted copper coin but am wary of deforming this. Again no movement. I have already had to carefully flatten the gearbox case gasket face as a straight edge showed some deformation (a sheet of toughened glass with wet and dry paper is perfect for this). As I wish to repaint and bake in a moderate oven getting the rubber seal out makes sense, replacing it would then be a no brainer. From the workshop manual a hammer and appropriate bolster looks like the answer? Any help anyone? See pics.
oh dear. technology seems to be a bit wobbly. Just the one pic
There are no oil seals anywhere inside these earlier gearboxes. The only RUBBER seal is fitted on the outside on the prop shaft which really only acts as a grit seal and nothing more.
Before you try and completely strip the gearbox, firstly have a close look at the pinion and check for how much play is in the square shaft for/aft/left/right. If it still feels nice and tight then leave well alone as it will only cause you problems further along.
If however there is lots of play, HEAT (and plenty of it, don't be scared to get things REALLY HOT) then find yourself a suitable drift and bash out the pinion gear while the casing is still hot/warm. (i use half a slab of railway sleeper with a hole drilled in it just for this purpose)
Flat edges to the casing can be re-worked on a flat surface with emery paper. (pump housing flatness to the sealing surfaces is always a bit wonky hence why the gasket is quite thick to take up some of the discrepancies)
The second weak spot on these boxes is with the prop shaft bush. Same thing, check for play up/down/left/right etc. (dont worry about in/out play on the shaft) Have a close look at the prop shaft to see how worn the shaft is around the bushing.
As these early boxes are designed to run in an emulsion of water and oil, you have to expect some leakage of water/oil past all the bronze bushes.
Oil is far cheaper to buy than new gears/pinions.
Going by the pics your gearbox looks to be in good shape with very little internal corrosion. (i would just clean the inside then re-assemble)
By all means re-paint the outside, but unless there really is a need to pull things apart further, this could lead to problems later on.
Many thanks for this excellent advice. Saved me making a mess. What I thought was a rubber seal is in fact the bush as I now realise when giving it a prod with a sharp instrument. It can stay there, a little leakage of oil to deter rust on the main shaft is a bonus.