2003 Johnson ST 6/8 HP 4 Stroke Outboards Service Manual, PN 5005471, Page 205Get this manual
GEARCASE LEAK TEST PROCEDURE If pressure gauge indicates leakage, submerge the gearcase in water to determine source of leakageIf the gearcase pressure gauge does not indicate leakage, increase pressure to 16 to 18 psi (110 to 124 kPa)Check for leakageMake necessary repairs and repeat test
Complete successful STEP before proceedingInstall vacuum test gaugeApply to inHgof vacuum (10.1 to 16.9 kPa) with pumpCheck for leakageIf leakage occurs, apply oil around suspected sealIf leak then stops or oil is drawn in, that seal is defectiveRepeat test, gearcase must hold minimum of 15 inHg(50.8 kPa)