It's a blown Injector seal at base of one or more injectors.
It's possible to diy repair if you're reasonably handy. Remove the injector (google this, it's easy enough, if stuck wiggle out while applying upwards continuous pressure using a 14mm spanner on injector body)
Once out, clean injector and remove lower copper washer seal. If copper washer is not on base of injector, it's stuck in the head. You'll need to fish it out using a long tool, Google can help here too.
Replace injector seal with new one and refit everything. Tightening down the new injector to the correct torque is important. If you don't have a torque gauge, make sure it's a little beyond "very snug"
Good luck
