Hello, I experienced similar symptoms with my Neorest 600. Do not call a plumber, they cannot fix!
I recommend calling Toto! Their support people will take the time to help you [this is what the experienced Toto plumber did that I hired :' ]
I had a leak too and ended up sending the whole electronics & seat in for repair. These one piece units do not require a plumber. Lo [Toto technical support] gave directions that I, a 60 year old woman who normally does not disassemble such an item was able to perform!
I realize some may not like my post to turn it to the manufacturer, but in this case it was the best solution for my fix.
Call first, get a case number and support person. Then they work quickly via email with you. This was my only toliet :' So i was with out a toilet during this period. Toto worked quickly to get my toilet back to me! The shipping time is what took the longest. Take a photo of the problem and you will be able to submit for your case via online.
Hope this helps! And hope your fix they will be able to send parts for so you are able to fix!
My excellent contact.
Senior Technical Support
(888) 295-8134 ext. 1641Office
(888) 295-8134 ext. 4Tech Support
5351 Jurupa StreetOntario CA, 91761