Ant:
The jerico has
oil cooler fittings for the cars doing enduros. If you are only doing 20-30 mile races, don't worry about it. If you want to know the temps, get an inexpensive infra-red gun, and take readings after each session.
If you fit a filter, make sure it has a large enough cross-section so that it does not plug, example - Oberg makes a gearbox filter...