I tried royal purple and it was slightly more noisy and leaked for me as well. We could argue the reasons but bottom line is I would go back to GL-4 dino 90Wt and look at replacing the O-ring on the speedo gear holder. Leave the speedo cable attached, loosten the tiny screw that holds the retainer and swing the retainer out of the way, then use the speedo cable to pull the whole thing out so you can get the O-ring replaced.
Definately go back to the GL-4 90Wt gear oil. Synthetic is not good for the brass in your transmission. 90Wt will be quieter, it will leak less, and the brass synchro rings will be much happier.