Water pump most likely. Ive had 2-3 on previous vehicles where I could only smell the sweet syrup smell but never saw any puddles. It usually leaks from the weep hole at the back like stated above.
1951 3100
1984 C10
on this trucks the water pump seals go out and the house coupler at the firewall cracks as well. my bet is the waterpump to engine seals have cracked
6.0 MAX Blown
I have the Castech problem, goin to a dealer to c if theres a chance they will fess up with some new heads