Ford S-max LS RNS Audio Unit

Hi

I have a Ford S max titanium 2010 with the LS RNS Audio unit. 

2 years ago we didn't use the car for a few days and came back to the car to find the audio/navigation units was dead. I tried a few things but nothing worked and it eventually started working a few days later randomly.

Few months ago, we didn't use the car and the same thing happened, the unit was dead. This time, the battery drained twice and was changed twice over a matter of week. I read on some forums that it was possible that this was draining the battery when the engine was off. So we paid a garage £50 to disconnect and 4 months later, haven't had any problems with the battery draining.

We want to get this issue fixed. Ford quoted us £550 for a new radio, I'm not paying that. 

There are units like this on ebay for £170

http://www.ebay.co.uk/itm/Ford-Focus-S-Max-Mondeo-Galaxy-Stereo-Car-DVD-Player-Radio-GPS-Navigation-USB-BT/201387749871?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649

Are these any good? A local audio technician said he would fit for £50.

I've since read that this is a relatively known problem with this particular unit so was wondering if anyone had come across it and what our options are please?

Thanks