(swirly images and harp music dissolve to traditional pub scene.....

You are playing a Red (for arguements sake we'll use DNA), and the m/c is playing reasonably well, but not brilliant. A couple of number runners with no way of getting at the sevens, and a few 'multi red exchange' boards that don't lead anywhere.
As your money starts to get eaten progressively quicker, and the boards become less & less forgiving, it dawns on you that you've probably caught the arse-end of a streak. My question is, at what stage (if at all) would you bail out?
Having pushed £30-£40 quid through it and not seen the results that you expected, would you have the discipline to cut your losses and walk, or would you just press on in the hope of getting a quick steal and recouping some cash? I found myself in this situation earlier, and true to form I just pressed on, suffering a pretty hefty loss in the end. I'll be back there after work to try and recoup of course, but I can't help thinking I should have recognised the tell-tale signs and just walked with a £30 loss. Ultimately it practically wiped out my weekend's profits in 1 hour, so frustrating!
Obviously discipline on Red's is vital, possibly more so than for other manu's, but once I've taken a fair-sized loss on a single machine (especially after seeing promising signs) I seem to struggle deciding when to call it a day. Anyone else get this, or have any useful techniques for avoiding costly lapses of discipline?