The leakage you describe is very common but not in great quantity. My M2 lost 1 qt or less_year for several years. You need engine oil pressure to run some functions but I don't remember which ones. The service manual covers this in depth. I don't recall a port plate on my 1980 l2 but mine was hydro.You have a good machine that will perform well if it gets reasonable care. The variable speed hydraulics never wear out. Watch the bushings and pins in var speed.