depending how worn the the frame is from where bolts have been tightened up over the years/months and if you have a deng rear hub, like where the axle slots in the dropouts, i found on my mates bike that the right side bolt was clamping the hub axle but put a spacer in between the the hub and frame and the axle bolt now clamps the frame and his chain is no longer slack
buy one thats around a year old that way it should be all bedded in and service it if the last owner dent get it serviced for a while and you have an amazing hub and you save money
yeh me and my mate ride there some times when waiting to get on the train for morecambe(like an hour wait sometimes) we just go down a hill outside station past this like "posh" part lol and go to the premier shop and round the corner is some kid/playgroup place? think its shutdown mind but, out side theres good to ride, aint there a thew riders in lancaster? i would'nt mind going there for a decent ride one of the days
ite sam, your back brake seems to work very well, like whats been said get your butt over the back wheel more and absorb the drop more, you'll get it soon am sure mate, you seem to learn well and listen maybe take some air out of your back tire?