I really should know this, but in 8 years I've never serviced or replaced my pedals. The RH one is fine – still spins smoothly with very little play – but the LH (non drive side) has a lot more play. It still spins with no grinding or hassle, but there's a lot of wobble in the spindle.

What's this saying about the bearings (or any other parts) and is there a rundown somewhere of how to repair/ replace them? Although they are ancient Shimano M515s, so I suppose I could just replace the pedals…

I dont know what an M515 looks like but a nice shiny new set of 520's is under £20 with cleats, I think you have had your use out of the old ones..

tinsy +1