I would HIGHYLY recommend NOT to use a tape cleaner in your eqpt. Please have that camera cleaned and inspected at a pro house. It sounds as if:
A) your audio record heads are not making the connection.
B) you’ve got a bad connection in your on cam mic
C) your tape transport needs aligning
I had a camera take a small tumble once and it appeared to be fine. I tested with tape/test shooting – all seemed fine – but after recording an extremely important event I discovered to my shock a once in every five minute or so complete audio droput that would last 5-10 seconds. I’ve had that camera repaired – but to this day – do not trust it as an “audio” record device. It’s strictly B-roll. How many events could your company survive a “no audio” disaster. (Don’t test this at home)
Hope this helps. Kind Regards, Chris K.