Two alternatives come to mind:
1. Plenty of masking tape, plenty of newspaper and a cheap tin of matt black spray paint, just clean the surface first with alcohol wipes to clean off the countless ideas and products that you have tried before.

Many national based pound shops like "poundland" sell the matt black spray for: Yes you guessed it..... £1.00:cheese: and just as good as a £7 spray can!.... Even if it starts to fade after a year or two, worth the time and money to do it all again, why waist money on products that work for 10 minutes or until it rains?
2. If you don't like the idea of spraying, try self adhesive vinyl.....
Many sites on ebay, easy to fit...Many colours and textures to use , even carbon fibre effect.
Total cost is around £4.00 average per meter... You only need 1x1m maximum.
I use a small amount of washing up liquid5%/ water95% mix in a spray bottle on the adhesive side to help with squeeging out any air bubbles and to aid positioning/ re-positioning before it dries and sticks (it does stick!)....
Leave for about 45 minutes until the adhesive has took effect with the drying out stage and trim off the excess vinyl with a craft knife...
Try not to bend the vinyl around the lips of the door edge, it never works and all you will eventually do is catch it and it will start to peal away..... very annoying!.... Just use the edge of the frame as your trimming line with the flat of the blade running against it, leaving a nice tidy edge that you won't catch.....
Dont worry, it is safe to wash and even jet wash your car the next day... just don't be silly and direct the pressure lance right on the edge of the vinyl, Simplesssss! :thumbs:
There you go... Two permanent solutions and also saved you money in the long run... I don't fancy putting nut oil on my door frame strips... Not unless I was "frying tonight":lol: