Cleaning the heads is easy with a DV tape head cleaner, it runs through the system and cleans it correctly without damaging the unit.
You can run it through again to make sure, but these can be purchased from online (MINI DV tape head cleaner).Now the reset reverting back to :-:—:—:— , this seems to have lost its parameters, so the internal cmos battery or capacitor that keeps the settings and date and time, usually when you are able to put a new camera battery you can set the date and time this should then be ok.
But I have experience many years ago with MINI DV, and converting them over to digital strorage , the heads would only need cleaning for the amount of time and tape ran through the system, the environment dirt the unit picks up also, so you would see your video but would play with instability and lines across the screen, or moving rapidly and giving a poor picture on display.
11 tapes to run through either 90 mins , 60 mins each is a long time so it could be heat related (possibly) as it’s an old machine but that really shouldn’t make a major difference, as these either work or not the unit would have in the settings log details to how many tapes or minutes has run through its life.
I would use a fully charged camcorder battery and clean the heads using a MiniDV tape head cleaner and run it through 2x.
At least you get to keep the head cleaner
I wouldn’t use IPO (alcohol) as it’s abrasive on plastics and can damage the unit.