Are there any known maintenance issues with older Mooney wooden wings?
You may want to look around here or here or even here but the short answer is they are a wooden wing airplane that comes with all the issues a wooden wing airplane does. One of the major things to look out for is the M20A's that had a wooden tail, those should generally be passed up on. The later planes should require some inspection of the joints where the tail meets the rest of the airframe as it is a stress point (if memory serves). For what its worth you are better off with a metal mooney. With a wood plane you need to inspect for rot the way you would for corosion on a metal plane. 

Like any wood aircarft the M20A's can suffer from delamination which would need to be checked for. unfortunatly the list of people that still work on wooden planes is dwindling with time so it may be hard to repair this. It would be well worth the effort to seek out a mechanic that has experience with the A model and can work on a PPI for you. 

You can find all the AD's for the M20A here.