[Welsh Anorak]

In fact Tim's 'quick and dirty' method often produced better results than the 'correct' method, especially on a well-worn machine.
To get back to the OP, I'd check the guides are going home - it's possible for one to be one tooth out and not fit snugly into the V-block. Also, if someone's been there before you then who knows what's been twiddled or broken, so maybe back tension issues might not be so far fetched.
Now Tim, you surely wouldn't align a B&O like that, would you?!