Check the Breather is not blocked with soot from the blow-by.
Any, and i mean ANY blow-by will make a labyrinth seal leak oil, if not well vented.
The Factory breather pipe is quite small, you could add another breather to
help reduce the pressure in the sump...... either in the other "Side plate" , or in the Rocker Cover (i think the the 3Cyl UR1's had a breather in one rocker cover, this cover will fit all UR1's, but not sure about Cristal.
Other possible cause of Labyrinth seal leaking is Worn main bearings,..... was there any sign of ware on the old labyrinth? if so the main bearings need looking at as there should be no contact between the labyrinth and the crank if the bearings are holding the crank properly centered...... Main Bearing clearance should not exceed .003" (or 0.12mm).
As a last resort, plumb the breather back into the intake manifold (between the air filter and the engine) this will help evacuate the fumes from the sump (and re burn them), but be sure to fit an oil separator in line to prevent "runaway" if too much oil is sucked in!!!!!!!!!!!
Use all 25mm plumbing in breather to minimise restriction to flow.