This is one of those judgement calls, I'll have to leave to you.
My honest opinion, its time for a new machine.
Options:
Change the heatsink, one the will accommodate memory expansion
check if lower profile memory is available
With core i3 - maximum memory speed supported is 1666Mhz
The v1.3 rev board does state support for single channel, but Installing a single stick of RAM in a dual channel configuration might not work, so be prepared for that. If you do try and install a single DIMM into the available slot, make sure it is the same speed, voltage, timings and density of the existing modules as this will be challenging for the board in the first place.
I only see revs 1.0 and 1.3 on the US site?