Morris Minor Owners Club

How often do folks have to top up their dashpot oil? I seem to have to top it up every few journeys but then again I might be overfilling and wasting it. I have always topped it up to the lip in the chamber where the piston enters.

What happens if the level drops too low whilst you are driving? Would it cause the engine to start running 'lumpy', lose power and eventually stall?

Yes, top it up to the level of the inner lip. As the oil runs low, there will be hesitation on acceleration and, eventually, the car will just stall when idling and trying to take off. Recommended check is every 3,000 miles. If it is over-filled, the excess will come out the little hole in the top of the plunger.

Aye usually done every month or two, to just over the top of the hollow piston chamber.

So, having topped it up on Sunday I checked the dashpot level again today and it has dropped. There is still resistance to the plunger, but the car hasn't even been started since I topped it up so is it normal for it to just drain away with time?

So long as the piston tube is full of oil that is all that matters.
Any oil above the piston tube will be wasted.

Just use a 20/50 grade engine oil - no need to use any special oils.