Internal Coolant Leak (Edelbrock Air-Gap Intake)?

[69 Short Fleet]

Hi, my rad coolant level has dropped twice in a row due to an internal coolant leak . The rad level is approx. 1/3 full, I never had this problem before until I installed the Edelbrock air-gap intake manifold, and I'm darn sure my block and heads are not cracked as I've never had this problem before. So I'm wondering if I didn't use enough RTV sealant around the front where the water neck location is (on the block). I'm thinking that it may be leaking internaly on the rear of the water/coolant hole (the main one that is part of the block). I put RTV sealant on all of the bolt threads and also around all the passages. Has anyone every experianced this before. I'm kinda choked as I just pulled the intake a couple weeks ago to fix an oil leak at the rear of the intake . Any comments are greatly welcome, thanks Doug