Actually the pipe has disintegrated where it enters the offside rear box. Run back from Heathrow this morning, I detected a rise in volume which was out of character!

Can this one box be replaced on its own or is it recommended to renew the pair?

Looks like a minefield on Ebay so would be happy to accept any recommendations.

I've just noticed that Rimmer Bros do a mild steel pair for about £115.00 + VAT.

Are these any good? I know that some aftermarket parts leave a little to be desired!

Separating the join was a major faff when I tried to just replace one, bloody rust welded together.

Best to replace the pair. Not only will the joint be rusted solid but you can almost guarantee that if you have different makes side to side you won't be able to get them to hang evenly.

Will do.

My advice would be to avoid Klarius. The first backboxes lasted just under two years before the stuffing started falling out, and the replacements lasted just about the same. The inner perforated pipe rusts out and then the fibreglass ejects itself.

Klarius is Eurocarparts own brand so unless bought from them, it won't be.