There are three main oil seals in a Vespa engine:

• Main bearing oil seal (at the crank): Keeps the gearbox oil from mixing with the oil/gas mixture.
• Flywheel side oil seal (at the crank): Keeps the oil/gas mix from the outside of the casing.
• Rear wheel oil seal: Seals the gearbox oil around the rear axle.

There are also some more minor seals around the kickstart quadrant, the clutch cover, and the rear wheel back plate.

The main seals should be replaced every time the engine is taken apart as they are cheap to buy but they are buried pretty deep in the engine. If you have the engine apart you might as well drop them in.

Clutch side seal: The clutch side seal on an older model large frame bike is different to the P series equivalent. Older large frames have both bearings lubricated by the gasoline/oil mixture. On P series bikes the clutch side main bearing is actually lubricated by the transmission oil because the oil seal is located between the crank and the bearing...Anway...

The following images assume you have already dropped the engine, split the cases, and removed the clutch & crank.

There are two ways to remove the clutch side oil seal. One is banging it out towards the flywheel along with the main bearing. The other is prying it out towards the clutch leaving the main bearing in place. Above is a shot looking through the clutch cover opening at the rear side of the clutch side seal. Whatever method of seal removal you choose, if your bike has an automatic oil mixing system gear (autolube) it is a good idea to remove it as it is very fragile. Use circlip pliers to remove the retaining clip, and be sure to keep all the small washers in order

If you plan to leave the main bearing in place you will need to remove the two bolts and washers that retain it from the clutch side and pry it out that way, or the other method (as I did) just use a large socket and bang both the bearing and clutch side seal through the casing in the direction of the flywheel. This method should be used if you plan to replace the bearing and the seal.

Once the seal is out throw it away. Clean the area all around where the main bearing and seal go. Be sure to have a look in the casing area and locate the lubrication hole to make sure that the hole is clean. It is drilled through the side of the main bearing hole. Blow through it with air if necessary. If this hole is blocked your bearings may not get proper lubrication. The oil seal is made with a special cut out for the oil casing hole (as seen above).