Coming closer ;-)
The 8 knots are stated in the QRH as a supplement for a flap selection less than full flaps.
Actually it is 7kts for flaps 30 instead of 45 and 14kts for flaps 20 instead of 45.
This is stated in the QRH for non normal operation like single engine (F20) or stuck Flaps etc...
Now I wonder if if you would basicaly say:
Ok, Flaps 30 instead of 45 gives me an additional 7ktd as per QRH + the 20 addition due wind from the example above... Or you say:
Well I have an additional 20 anyhow and I dont care about the 7 from the QRH.
But as those 7kt are related to performace and the 20 are related to weather, I guess you are better of to add both to a maximum of 27 what you do for example in this situation as well:
Singe engine - Flaps 20 - Vref plus 14.
In case you have 30 gusting 45 you would take:
Vref 130 + 15 (half steady wind) + 5 (15kts gust but as to max 20kts its only 5 knots remaining) + !!14!! (for the flaps 20 situation) =130+20+14=164