I have individual primary pipes on my pretend Cobra. Several years ago I tried the red RTV because of O2 sensors recently installed. The RTV was a fail for sealing.
I've had the pipes on and off many times during 27 years of ownership. The easiest side pipe installation for me has been:
a. Bolt on the the individual primary pipes, leaving them somewhat loose.
b. Use wood blocks to hold the side pipe in its almost-installed position.
c. Spray the ends of all pipes with a bit of WD40 before insertion.
After steps a., b. and c. I can get a side pipe and the 4 primary pipes joined in 1-2 minutes. Occasionally a bit more time.