He grabbed the bar for support as he shifted his bottom onto the nearest stool, relieved that none of the old timers currently propping up the bar gave him a second look. Jeff waved a hand at Sally who was busy washing down the bar. I have used the word 'bar' too many times here but can't think of another word to replace it! My character has just walked into a pub, is there another word for bar ( I thought maybe counter but that doesn't really work) or another way of describing what the barmaid is doing?
You may want to rephrase that first sentence - have him shift onto the stool first, then the grabbing the bar - then rephrase the next part substituting "it" for the second bar ("it" would then refer to the bar, not the stool). For the barmaid, maybe use "surface", although I see nothing wrong with "counter" either. (Oh, and I'd drop "his bottom" - what else would he be putting on the stool?)
'He grabbed' sounds to me as though he is stumbling or near fainting - fine if that is the case, if not I would go with something like this; Taking hold of the counter for support he sat down on the nearest stool, relieved that none of the old timers propping up the bar gave him a second look. and to get rid of bar from the final sentence, Sally could be rinsing glasses, pulling a pint or slicing lemons.