A couple of things:
Planking is caused by the expansion and contraction of the timber PF... it cracks the paint along the grain. Often this  cracking is very small and if on darker colours then it can be painted out quite easily. What you do have to do first though is try to get any dirt and grease out of the cracks, so Magic E and Meths is good for this.. work along the grain, not against.
Personally, i dont use water based acrylics as the drying colour is darker than the wet colour.. it can take ages to match a colour perfectly with water based.
Enamels are my favourite,,, very easy to mix, colour doesnt vary with drying and they are readily available... drawback with these is that it takes a whole day for a single colour to dry which makes for slow progress.
A compromise is made here and so i use acrylic lacquers.. they dont mix so well and you have to have more tints as base colours.. they dry VERY slightly darker than the wet colour and they dry really fast and so good progress can be made with these.

When painting the PF.. you MUST give the paint something to grip to. So a light sand is required.. if you use enamels then mix a little Penetrol into the paint.. it helps with the grip, or you can wipe over the PF and let dry - both will work well.

decide before you start as to what final finish you are going to use... Mylar, CC or even Polyurathane works very well. If CC or PThane then you have to mix your colours to how the PF will look once protected... this is especially important if you have given it a light sand and so now have a misty effect on it. Its easy to replicate the colours.. dab some spit on your finger tip and place onto the area you are trying to match... this is how it will look with the final coat on and this is the colour you must match... its a leap of faith to paint an off colour.. but once its cleared, its invisible.. trust me..LOL.

Now then.. planking..

With darker colours i normally make a wash up.. this is just a thinned out paint and i paint the whole area with a soft brush.. its very quick to do, deepens the existing colours and after a couple of washes, the planking is gone... clear this and it all looks 100% again.
Planking on the off white is a different kettle of fish as the dirt shows up like dogs testicles and so for the white, i normally match the colour and airbrush the entire area/shape... its the only way as a brush will leave noticeable drag lines. This " white" is NOT white.. there is no white on a pinball... often its a base of white with a lot of yellow ochre added and sometimes just a touch of blue or red... you wont believe how brown it looks in your mixing jar, but once added to the PF, chances are its still too light. your eyes will lie to you with this colour... keep getting it darker until your colour spot/dab blends into the existing off white... paint it too light and it glares out of the PF and just doesnt look right.

If the planking is so far gone that the paint is curling at the edges, then you could be in for a lot of work... paint your wash as normal and then CC over the top or P'thane.... apply several coats to build up a decent level and then sand back to smooth... the CC will seal whats left and you are sanding off just the tips of the curled paint... you can then apply the wash again if necessary and then a final finish coat.

Hope this helps.. and best of luck to you!