Potentially I thought I might need a replacement washer nozzle (the one with 2 jets underneath and the 4 rubber duck-bill outlets).
On ebay they are incredibly rare if you can actually find one, and if you can, they're very expensive, circa £50 upwards.
I discovered if you look for a second hand wiper arm at a fraction of the price, circa £12, they often come with jet still attached to the arm.
Nice!