In reply to Timmd:
I have a Berghaus Dart 45 which I love to bits (literally) of a similar vintage to yours (probably purchased around 1994/1995). I once tried to replace it with similar, and happened to go into the (as was then) YHA shop in Leeds. Got chatting to the manager, and he said his wife had the exact same model, and she wouldn't let him take it off her when he suggested replacing it: he recommended I should keep mine, describing it as "bomb proof".
Mine is still going. I get bits of it repaired, replaced, patched periodically (usually straps & stictching). All my walking partners chuckle at it describing it as an antique (the rucksack and the wearer!).
I get stitching repairs done at the local cobbler in Settle (Nelsons) as they have the equipment to do the strong stitching and are very competitively priced (and just round the corner). Any technical repairs I use LSR in Burnley where the people are lovely and resourceful and imaginative when it comes to repairs; they used to look at my rucksack like a timepiece, but after a few times of seeing it, they just sigh....
Not really a direct answer to your question, but tangential and sharing my experience of similar repairs.
Perhaps there should be a congregation of Berghaus ("they don't make 'em like that any more.....") packs on a hill one day....