Ok, so I have a reverb, working ok, but I shortened the hose at the seatpost end and tried to reuse the barb, it is OK, but I think that it will need replacing as it is leaking the tiniest bit of oil. Anyway, the issue is that the barb will not come out of the seatpost, it is totally stuck! Anyone know anything I am missing?

It won’t be the barb that’s leaking, it’ll be your where the hose meets it. Try trimming the hose square with a really sharp blade, or better still a wee hydraulic hose cutter, make sure it’s clean, and refit.