Having stripped and cleaned them I’m now reassembling with new o rings everywhere. All going well but I now have oil seeping out via the lowest damper seal. I assume this shouldn’t be happening, any idea how to fix it?

Anybody???

Sounds like the o-ring has been pinched or is the wrong size or undersized (it happens sometimes) or you have fitted the wrong one. What ever it is sounds like you need to fit a different one.