It would be best to check your manual or contact Prochem Europe about service intervals Brucie. (0208 974 1515). The usual things to check and/or replace at service are Carbon brushes to all motors and clean any deposits from cooling fans. Clean/replace any filters as required. On my machine with 7.2" vacs service is at 300 hours. Most machines with 5.7" vacs can go longer. Service is also something ongoing. Each time you wrap up a power cord you should check for damage, and periodically check plug connections for security. Clean out your recovery tanks regularly and certainly after a particularly dirty job. Lubricate QD fittings at least weekly with a silicon spray (NOT WD40, this will eat the seals) Lubricate the dump valve seals and guillotine shaft also with silicon spray. Ditto for valve stems and QD fittings on tools and hoses. Clean waste tank filters daily at least. Plus anything else you may notice. Never leave things undone. They wont get better on their own.
Safe and happy cleaning:)
Ken