I have to chuckle about the reliability of the 603 with the aluminum head and the 617 with the cast iron head. In theory I completely agree with the reliability of the 617. Just bulletproof with the cast iron block and cast iron head. I recently acquired the 603 in the SDL and it runs perfectly. So, just recently, which one begins to have head gasket problems? Unbelievable, but it is the 617! Pressurized cooling system and continuous loss of coolant and traces of antifreeze in an oil analysis. Not much more you can say

Maybe the 617 has decided to shove it up my *** as payback for purchasing the SDL?