Got it!! Yeap that was it. Took quite a bit of pressure, but finally my screwdriver got through...lol
It's amazing how hard that accumulated crap gets after 19 years of never been properly drained. It literally felt like a solid metal wall...
Sprayed some PB Blaster in there to try and get rid of the rust build up inside the block. Will finish flushing it really good tomorrow.
Tks guys...