Sapper don't buy a carby, I just picked a PT up on hard rubbish 5 mins ago, just keep a look out they are still out there and people still chucking them out, although not like they were a few years ago.. Once a few people know you are playing with them they also look out for you, that helps. I haven't seen a pic of your broken decomp port but if it is just the white end that has broken don't worry about it .
MF that is a bodge done by somebody to keep the cable in place. Pity you aren't closer I have boxes of those carbys but I will not post any thing any more