My first Savannah is an 11 year old F2, so I know what you mean about them not slowing down with age... they just never seem to completely grow out of kittenhood
The spraying was definitely what you thought it was, marking his territory...your home may have smelled like the previous cats a bit for example and he had to lay claim. I'm glad with some persistence (and cleaning) all calmed down which is exactly how we'd hope it would go!
Some of the group might be interested to know that Rock Star is one of the very first Wagati F1s... Nicole Greig of Wagati produced some of the first F1s and many many of our Savannahs go back to a Wagati F1, my very first breeding Savannah had a Wagati mom Nicole actually took him back to foster while we found his new home, how cool that must have been to see one of her babies thirteen years later!
Wow, that is truly amazing! So Rockstar is 13 yo? How awesome!