Hi - I have just finished painting walls in a bedroom. On one wall there are 3 small patches (Not big but noticeable) showing up. I tried putting more paint but they just reappear!! I suspect it could be small patches of wallpaper paste I havent washed off properly (what a plonker). Is there anything i can do except rub it off and start again???? Would i be able to use one of the Zinsser products?? There are s many to choose from - all very confusing to me. Could someone please offer advice.Thanks