SEGA Multi Mega Freeze & Reset

Hi folks,

Only recently joined - but I've added a small section to our "New Members" section.

Well I've waited almost 20 years to own a Multi Mega and I finally managed to score one from eBay at a very reasonable price. "Fully Tested and Working" = Awesome!

And then I received it and that's when AWESOMENESS turned to SHIT.

Essentially when I received the Multi Mega I noted the following three issues:

1/ The unit worked fine for about 8mins, but half-way through the first level of Golden Axe (CD) the system froze. After a reset the system would not boot beyond the MEGA CD animated logo and kept auto-resetting. I left it for 30mins and tried another CD game. Again it worked fine, but only for another few minutes. I read that this could mean weak/faulty capacitors (it is 20 years old!)
2/ The AV port itself was temperamental at best - I had to very carefully manipulate the cable at the unit end to get any picture on a TV (I purchased a new RGB SCART cable, thinking it was a cable issue, however the problem persisted.
3/ I also had to wedge out an old Duracel battery that had rusted itself to the inner battery compartment of the unit - this had obviously been there for quite some time and had actually eroded the battery contacts.

Because I opted to fix rather than complain to the seller I've now missed my chance at a refund (stupid I know - but I just wanted a working unit)

Any how based upon what I had read on other forums I sought about getting a retro-tech to fix the issues. So far this is the work that's been done.

Cleaned and treated eroded battery contact points.
Replaced a faulty AV port.
Replaced all internal Capacitors.
Replaced Megadrive system video RAM module.

However the issue still persists. Which brings me to some questions:

1/ Has anyone else encountered this issue? What was your solution? Most folk experience a weak CD Lens and have to either replace it or mess with the POTS.
2/ Are the Video RAM chips from a MEGA CD (1 or 2) compatible with a Multi Mega main board? I ask because it's been suggested that either a replacement Main Board or replacement MEGA CD Video RAM chips is required. However I would imagine a replacement Multi Mega board is about as easy as buying a Multi Mega itself.

Any help or advice about salvageable parts on offer would be awesome guys.

Thanks