Can anyone give me a general maintenance schedule for a diesel forklift?

I have 2 diesel forklifts (an old Clark 20,000 Lbs. & a 1999 Waco 10,000 Lbs) and none of the owners guides have a weekly/monthly/yearly maintenance schedule. I also have an old propane CAT 5000 Lbs. with the same question. If anyone could share their knowlege of when to perform and what to perform as far as routine maintenance I could really use the advice. Thanks so much.