Jon,
Are you sure it is a crack? It is in the location of the reverse idler lock pin. They have a tendency to leak. I would clean off the paint around it and make the determination. If it is seeping around the pin, a little JB weld should do the trick.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine