Agreed. Get an 8130-3 form (about £50 from the avionics shop) plus a letter saying it worked when removed from the aircraft, and flog it on
US Ebay e.g.
here.
But beware as Americans are suspicious of Europeans selling bad stuff. One nice chap (who bought a few bits of mine) described how some French sellers sent bricks to American pilots. So describe it very well and honestly, with plenty of close-up pics.