Brake booster issues

[ken riverina]

I have 1985 gx diesel cruiser. 210,00 tar road km. I had a booster fail and changed it over from a wreck. The failed booster had a lot of oil in, 400ml aprox and also the clutch booster had some oil. No oil was found in the pipes from the vac pump, no smear even. I cant work this out? maybe the times at full temp, the mist of oil vapours passes into boosters and then liquifies? After this change i noted the pedal often went about 70% down in travel rather than 30% aprox. This is intermittent. I changed the master cylinder as i thought it may be the case, but it still has the intermittent pedal distance travel.
Can somebody tell me what is the cause (brakes work well regardless of pedal travel) of this pedal travel changing?
Why is oil getting into the brake booster. It is not brake oil and could only be engine oil.

thanks, ken