Do I need a re-entry permit for the non-immigrant type OA visa when leaving Thailand?

Now that the non-immigrant type O (multi-entry) 1 year visa is no longer available, I've been considering the non -immigrant type OA (multi-entry) visa - I'm over 50 and retired. So can you clarify please: if, during the period of the visa I want to leave and re-enter Thailand, do I need to complete a re-entry permit? (being multi-entry implies not but have read some conflicting articles). And for each 90 day period, do I just have to go to the immigration office (with forms and documentation) rather than having to leave Thailand? Apologies if all this has been asked before, but unable to find a spcific thread. Thanks in advance.