hey ariston -
awesome you and shutterfinger were able to rehabilitate the shutter !
i think what you might be able to do is just pull the dark slide out incrementally like a "test strip"
or cover the lens incrementally with the dark slide ...
just remember to cover the lens/ take it off bulb/time when you re-wind the shutter to make your 2nd/3rd and 4th exposures
it's too easy to forget to do that ( been there done that ) / kind of a homer simpson
d'oh! moment when you forget
what i've done is 1/2 a sheet of film with the FP shutter, and the other half with a behind the lens shutter to see how close they are on the same shutter speed.
FWIW, i always "err" on the side of "too much light" ...
have fun !
john