hi guys
My mechanic said one of my engine values is leaking, and I should get it fixed at an engine repair centre. Then a yellow light like a coil started flashing when I was down in london.

I was able to drive back to hull, but gears 1-4 were sluggish, lacking power, but 5 was ok and it seems to be ok around town, but only comes on and gets sluggish on the motorway
I was told one of my valves was leaking and had been leaking for a while and I need to get it changed.

Its a 2.2 honda accord diesel.

I was hoping to sell the car this summer, but wanted to get advise first
many thanks
E