My '40 has the same defect ,, so did my '39 .... yes its terminal .... the block cracks there 'cause the water gallery is blocked at that level with rusty crud . It is very hard to clean it properly to do a neat repair , the block is rusted thin there .
Having said that ,,,, I have been running my '40 like this for years , just keep a close eye on the water level .
On the '39 , I welded the crack using castiron rods ,,,, today , a mig would be a better deal .. I only welded it cause the crack was so big ( 8 " ) . Sealed it with some chemi weld
Confused ? ...... :p never mind , fix it if you want , or , leave it if you want .
