Remove all traces of the old gasket from the pump and engine, using a paint scraper if necessary.
Tighten all fixings in sequence to the correct torque (consult a service manual or dealer if you are uncertain of the torque).
After the oil seal is positioned in the groove, apply even pressure to the oil seal using a seal driver or a similar tool. This will help to seat the oil seal firmly in the groove and prevent it from moving during use. Make sure to apply the pressure evenly and gently, as applying too much force can damage the oil seal or cause it to deform.
One common reason leaking occurs in engines is that debris is caught in the fork seal, holding it open and allowing oil to sneak by. So, how do you fix this? This is where the little circular devices come in—oil seals.
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The most common oil seals are the ERIKS types R, RST, M and MST, which correspond respectively to types A, AS, B and BS according to DIN 3760/ISO 6194.

Refit the sump, taking great care not to disturb the gasket. Hold it up by hand and fit two front bolts and two rear ones to keep it in place while you refit the rest.
When the total eccentricity is excessive, the sealing edge of the seal lip cannot accommodate shaft motions and leakage may occur.
Total eccentricity is the sum of shaft runout and the housing-bore eccentricity.
Total eccentricity, shaft runout and housing-bore eccentricity are generally expressed in TIR (Total Indicator Reading).
Replace the sump drain plug tightly and refill the engine with the right amount and grade of oil.