It is not easy to build a completely leak-free Lotus Twin Cam. One of the key problems is an only-fair breather system. Then consider that high revs lead to higher than normal bore wear. Add in all the almost-fits adaptations to make a push rod engine into a twin cam, and it’s not really surprising that most leak.
First evaluate your engine’s condition. Compression and leak-down good? Valve guides (burns blue on start up)? If that’s ok, you could pull and re-seal the engine. Also gives you a chance to check the critical crank endplay shims. If the engine is worn, no amount of re-sealing is going to stop the blow-by pushing oil out.