Hi, I've done a bit of a silly thing, I was working on a seized rear brake caliper and took it apart, cleaned it (the seal was perished) so I removed it and to check it would go back in properly I put it back and now it's stuck, I've tried re connecting it to the brake line but as there's no seal it doesn't work, any help would be much appreciated, cheers

You can buy rebuild kits on eBay fairly cheap. If your not used to working on brakes, then get a new calliper, or get someone who knows how to rebuild them as at the end of the day they're what stops the car, so quite important.