Odd it has foil tape on switchbox and the clear potting leads me to believe it may be a chinesem switch box. Yank powerhead,strip it down, get a factory manual,bore all six, replace switchboxes,impeller and t-stat and reassemble
These rarely fail unless engine gets majorly overheated. 95% of oil problems on the 3/4 cylinder loopers are the magnet coming unglued from float in oil tank and warning modules.
Your 140 could have come with either the large or small gear case which both have the same gear ratio. The 1983 will be the small gearcase but will bolt up as DS length is the same.
