Are there any ideas as to what would cause the leak only to happen while the motor is being reved? If the seal was damaged and or installed incorrectly, shouldn't it leak at all times? Is it possible that it's a crankcase pressure issue that is building up pressure during higher rpm's?

I had had to redo same on my 440. My suggestion is to install retainer without side seals. Retainer channel in the block must be cleaned of any oil residue. Without side seals lets the retainer find its neutral position in relation to the seal so in other words the seal is aligning the retainer front to back position. Then Fill the side seals with RTV. But you may say "how to do that with engine in car and clutch in place. Use a 10ml Syringe with a small gauge luer lock blunt needle or a meat marinade injector needle. Don't use the big marinade syringe, keep with the 5ml or 10ml size one. You can get these items from amazon.

https://www.amazon.com/gp/product/B07L2TXW1C/ref=ox_sc_saved_title_6?smid=A1IYIADSPFVZEE&psc=1

My picture in prior post you can see the gray RTV filling the gap between block and retainer.

Also, I used lock-tight 518 on the 2 ends of the main seal and put it at 12 and 6 oclock.