Thanks for all replies, comments & suggestions. Based on what everyone has said i think i will leave it alone for now (and suffer sore knees) we are only talking a need a raise it maybe 1cm – or purchase the same saddle as the original as an alternative. Hoping to replace the bike soon anyway.

@robinlaidlaw Sounds most logical answer, although last time i took one into LBS and asked for one they spent about 25 mins comparing and head scratching only to tell me it was an unusual size and they didn’t have one! So can it be that simple? I’ve had several LBS in the past tell me different sizes, all of which i’ve forgotten, but this is non drive side and not had one of those go before.

@druidH I fitted the last one myself, i don’ have a torque wrench but just tighten to what seems sensible, not over doing it. Not jet washing.

@bowglie I don’t remember any water in there, but you’ve just reminded me that both times they’ve gone, a few weeks before there’s been a brown liquid discharge from between the BB and pedal arm, which ends up all over the left pedal arm. I thought it looked like rusty water, but as it’s all alu i couldn’t work it out or where it had come from.

My original thought was a seal inside the BB had failed, maybe water getting in and rust is from the bearings? I do ride in all weathers and wash it a lot, but surely it can’t be that easy for water to get in?

Would definately recommend trying a new chainring

Right i’ll get one today! Thanks all.

Thanks for replies thus far, in response to some of these:

oxym0r0n – Doesn’t happen in particular gears, randomly can be any. Mech not stiff

Rusty Mac – Bike is not left locked up so unlikely to be bashed

boriselbrus – Could be the freewheel, i whip that off and have a look, sounds clean though

Mark N – still got the old cassette and chain, was pretty much the same reason for replacing it in the first place

BigJohn – Have lubed, but didn’t clean it first, will try.

orena45 – This is possible, the old chain and cassette was pretty worn out and the chain did come off yesterday, i only have two front chainrings so the smaller does get a lot of use, but it does feel like it’s happening at the rear.