Jimmy, we had a similar experience and found the oil was atf fluid leaking from the high pressure line on the auto park brake assembly. Workhorse cahssis. When it failed completely we had the parking brake locked on. Managed to get it released and had to chock the wheels to keep from moving when we stopped during the trip home since we couldn't find any service available on Sunday morning in southern VA and needed to get home for work on the next morning. I replaced the steel line that had rusted through with a high pressure rubber hose and all was good when we traded that unit several years later.