what year 518 M O
I have an early 3 wire Smaller dia shaft)with Diesel Planateries Diesel # of clutches half inch cooler lines with big cooler with 1/2 in and out. shaft opened up etc 250 k no more problems
if late with larger dia shaft then 47 guts and keep those thrust washers cool
do not believe in tubed cooler drill out the case for larger fittings and open up the oil passages