Oh, gaskets are sooo last century…

I'd suggest either a neutral-cure silicone 'instant gasket' or a non-setting sealant like Hylomar, or Red or Golden Hermetite (if they are still available). No cutting or fitting needed and no risk of moisture, absorbed in the gasket material, causing corrosion. If using silicone, only a tiny bead is needed (eg from an hypodermic syringe without a needle), around where the oil may 'come over the top'; be careful to get 'neutral-cure', otherwise it will be the type that releases acetic acid on curing which can cause quite spectacular corrosion (ask me how I know…).

I don't know the composition of Flexoid sheet, so can't comment on its suitability, but, if you want to keep the machine 'period', oiled brown paper makes pretty good, cheap, gaskets, when the mating surfaces can be assumed to be well-finished and flat. (Oiled so corroding moisture doesn't get in.)

My 1967 motor cycle did not have a gasket between the crankcase/gearbox halves. It did not leak.

One possibility is that you over-filled the oil bath? A better question might have been: How did they avoid oil leaks from this installation? Fitting a gasket may not be the correct procedure.

Just another thought, sparked by NDIY. The oil level should be about half-way up the sight glass (IIRC there is one…). I'd expect this level to be below the bottom of the semi-circular cut-out in the end of the casting – the worm really only has to dip into the oil. So is the leak in fact from one of the tapped holes, which has been drilled right through, into the oil resevoir? A bit of thread sealant will fix that.

As my above post plus only the lowest parts that rotate need to dip into the oil bath so maybe not as much oil as you think it needs.

Steve.

just use and RTV silcone sealant…u don't need much and it's what car manufacturers use now…..

get mine from the States……

u can even get it in dif colours as well as clear……

Forget the instant gasket,goes off quickly,most is usually wasted and expensive ,also instant gasket goes everywhere inside when squeezed and has been known to bung up oilways and get to places where it should not be, Comments like get with times and use modern sealants,its better to use methods that were available at the time of manufacture,though unfortuneatly some of the best sealants are no longer manufactured,ie Osotite,the various Hermatites,not because they were no goodbut because our engineering industries have collapsed the the demand disappeared,plus cars are now so reliable ,very few people take their cars or motorbikes to bits and repair them.A solution to the end plate sealing is to aquire some .5 mm gasket paper from a motor factor,our local factor sells gasket paper which is very tough and does not tear quickly,and and seal each side with blue hylomar,or do what garage mechanics do smear the gasket with grease, In my youth I thought using grease was not good practice as I had been shown to use Osotite and either gasket paper or if the machined surfaces were in good condition just Osotite with no gasket on machine tools.Years later I was involved with a friend who supplied recon motor parts to the trade ,mainly commercial water pumps and steering gears and he fitted thousands of thin paper gaskets smeared with ordinary light grease,with no complaints about leaks. On machine tools the faces to be sealed must be clean and flat and no burrs around the edges,rubb an oilstone over the surface,Leaks can be caused by areas around tapped holes where the holes were not sufficiently counter sunk prior to tapping and tightening the bolt causes the theads to lift a few thou and stop the mating plate sitting down, also there can be muck and old sealant around the base of studs which again can prevent the mating part from seating .to clean the muck from around a stud i use the point of a three cornered scraper.In the full size world I sometimes I get work where steam and water flanges leak ,the flanges are usually banana shaped where steam drivers in the past have had leaks in the past and used very thick gacket material bolted them up tight ,which only bend the flange fae a bit more, solution is usually face the flanges flat ,countersink the thread for the pipe and make sure the pipe is below the mating surfaces, very often over a 100 years of life the flanges are past it ,and owners get new flanges cast for me to machine over the winter break, and then assemble with thin gaskets.

I always go for Hylomar for metal to metal joints, you only need a very thin smear to fill the machining marks and you have plenty of time to assembly the parts. It has the benefit that you don't need to try and guess gasket compression when you are designing an assembly of parts.

You need to be careful if there are any nitrile O rings though, the solvent in Hylomar causes the rubber to initially swell, but as it disperses the rubber shrinks to less than its original cross section and you can get leaks. Not sure if Viton and Silicon is affected in the same way. You can get away with it if you let the solvent evaporate before assembly. Not an issue in your case.

I can't see if the tapped holes break through into the oil space, that will dictate where you apply your sealant. Oil will always find its way down the threads.

Neil