If the leak is coming from the top/lid of the pump you can replace the gasket without too much hassle, the gasket itself should be around £2 or so. The lid has three torx bolts and one security bolt, the security bolt can be removed with a 7mm socket hammered onto it.
You should be able to buy the gasket from any diesel/bosch/vag dealer using this part# 2 461 015 008-000