I emptied what was left into a glass and added parafin oil - it formed two layers when I first added it, but after I mixed it they didn't separate again.
Mine had a crack in the back membrane - I first tried to silicone it up, but after a few days oil came out under the silicone, and then the silicone came off in my hand.
Next I tried superglue gel (just being slack

) and that sealed well until it dried, then it cracked along the original crack.
Third attempt was 5 minute araldite, which appears to have done the trick - I suppose time will tell.
There's a small chamber at the top which traps an air pocket, which I'm hoping will deal with expansion/sloshing issues. I drilled a small hole in this to top it up once I had it reassembled - about 50ml of oil, one drop at a time.

I sealed the hole with silicone, and left a pin hole for the thing to breathe - I can't imagine that being completely sealed is a good idea.
I'm thinking about looking for a trip computer which might fit - anybody have any experience with such things? It's that or gut all three gauges and put a GPS in there? - but what to do for Oil Pressure and Volts?
Cheers,
Scott