Coolant Tank Cap Pressure

[TX '90 ZR1]

Weather was just too beautiful today so I couldn't resist going for a drive. As always, I check everything to be sure all the fluid levels, etc. are correct before firing up the "Z".
Noticed the coolant tank cap was a bit hard to remove. Appears the gasket is getting a bit dry. Don't know if it is original, but I think I need to replace it.
The present cap shows to be a 17 lb. cap. For some reason I thought they were supposed to be 15 lb.
Before I get a replacement I wanted to inquire as to the correct pressure cap to install.
What was the original cap rated ?
I did a quick search but came up empty handed. You "all knowing" guys always have a quick & correct response so I thought I would just ask instead of searching any further.
Also, does anyone other than me worry about damaging the coolant tank when removing the cap? I always support under the tank when removing the cap.
Thanks in advance for the information.
OH YEA, THE DRIVE WAS FUN!!