Similar for us.
No deposits for the bikes.

Driving a motorcycle on highways is indeed illegal, which makes sense as the maximum allowed for Iranians themselves is a 250cc motorcycle. Noone minded that we did take the highways though. People at toll stations were just very happy to see us and have a chat. Since motorcycles are not officially allowed there's also no price for it We got through free of charge every single time.

Passed a number of police cars on the highway and were never stopped, except once on a totally deserted stretch where 2 bored guys had been sitting all day in their car under a little pergola. They mentioned we weren't really allowed but were actually just more interested in where we came from and what we thought of the country. After a couple of jokes we were sent back on our way.

We did get 92 octane quite often. And even the occasional 95.