I think Brompton chains wear out more quickly than do my 700 c bikes' but they obviously have the chain higher off the ground and being single or IGH don't have a chain tensioner to get dirty either. In maybe 5k miles I have gone through a number of chains and one cog, although I use both a single speed ( the cog that wore out) and an SA 3 speed that hasn't yet. Cogs here are , I think, 8 bucks plus shipping so I buy a couple at a time. I wax the chains and try to keep them well lubed. I am clear the tensioner is needed for the fold but it does seem to be a dirt magnet. I have repacked the front hub a couple of times , which is easy to do, and the single speed breaks down to clean and lube the freewheel better than any other wheel I've owned. I had replaced the bottom bracket with a 119 vuelta BB for $13 and it has held up fine. I hated the plastic tightening rings on the original. I have used a Sugino RD crank with a vuelta chain ring but one tooth got chipped and I went back to the original swaged one which has held up fine and is really light. Are the newer 2 piece cranks as light as the swaged?