MPG down after injector seals replaced!

[Wooders]

I recently had my injector seals replaced and now I am only getting 32mpg per tank of fuel.
The car is a 2005 S40 2.0 TD.
Now,I don't nurse it,but for the past 5 yrs mid to late 40's was the norm.For the last 2 I have had a leaking injector,which I didn't worry about too much,until I learned the damage it could do to the head etc.
Had the seals replaced and low and behold,the valve seat needed machined,which was done.
Since then,no leak but low 30's mpg.

Anyone any ideas?

[Wooders]

Since last post,I have changed the oil and filter plus cleaned the air filter (K&N).
Tyre pressures all at 34.
No fuel leaks.
The only other difference is the outside temp is down from the -15 it's been for 5yrs to -25,with the '*' freezing sign on,which it didn't used to.
Not sure if the ECU uses that to calculate air density?