i just bought a 1978 Chevy sportscoach i drove it 75 miles to the RV park parked two days and the trans wouldnt engage. put fluid in and drove 26 more miles and parked tried to drive again and no forward gears. reverse is great but no drive gears. crawled under linkage all moving correctly do I just need to do a transmission service and dont know what type trans. it is. PLEASE some one help.