Heater Core on A/C Truck Questions

[Already Gone]

Removed my 50 yr old heater core and had it recored. When I removed the core from its 50 year place a bunch of goop, friend said was called Dum Dum and stuff on yellow rag, started falling out from various places where the core was. So I managed to get it back together today without the goop and am wondering if it is really needed ? The core is just slightly touchng the case in one spot, pictured, and wondering if this could pose a problem with case melting from the core heat. Also I removed the 2 relays from the corebox and wondering if should just reuse or replace. I took them off and detailed them and put em back on.