Sand off the old finish and apply what you like. I like to use a satin GEL polyurethane. It goes on supper easy with either a lint free cloth or a white scotch brite pad. 3 coats will seal and protect. There are no drips or runs, you don't have to sand between coats, but I run some oooo steal wool across the surface anyway. I use this stuff on furniture that I build, and it holds up really well. Give it a try. I intend on building hardwood cabs for my MKIV and thiele. I will used this as a top coat.
Boiled linseed oil, danish oil, varnish all work well also, but you need to recoat every year or so and they don't prtect nearly as well as urethane. If you use oils, make sure you spred out whatever it is you apply it with and let it dry before you toss them in the trash. Oils will occasionally combust when drying on a cloth just sitting there. Keep them out of your house and let them dry.
