Hello all and thank you for your replies. I'm in Hampshire, southern England - we use lbs and kilos interchangeably, sorry! he's about 60lbs.
Sebo is sick less often now - maybe only once or perhaps twice a week. But it's the fact that this came out of nowhere that has me worried. I asked the vet how or if it were possible his metabolism might have changed (with age?) - which got the 'one of those things' response.
He's been having the same two types of food all his adult life - both dry, one kibble, the other a muesli (though actually the latter is now a mature lite version, but the puking is much more recent than the change). That said we've decided to introduce a higher quality (much more expensive!) food (still dry) to see if that helps. We'll give him dry food for his bedtime snack too and cut out the wet.
Re stomach noises - no, that all seems ok - he poos normally too. One thing though, he does eat grass at every opportunity and often smacks his lips / swallows (like he's got reflux almost). He is on Rimadyl (and lots of natural supplements) for his arthritis so we thought it was a pain thing connected with that - but perhaps it's a tummy thing? oh why can't they talk!?
Thanks again for reading and your ideas. I think a 2nd vet's opinion is required.