Make sure you have a very good ventilation system (and a lot of spare time) if treating a piano for borer. It's quite a difficult, time-consuming and fumey job. I found borer holes in nearly every wooden surface, including some of the keys and even the loose block of wood I use to make reaching the pedals easier.
The process is quite simple. You need to pull the piano apart and put it on a drop sheet. Grab some non-staining kerosene oil and add the appropriate amount of borer oil. Make sure you are wearing rubber gloves throughout the whole process. Then inject the holes with the solution using a syringe (I'd advise against asking a chemist for one when you sport a vivid bruise on your arm from a blood test). Once all the holes have been flooded (including the ones you must get upside for), paint every accessible wooden surface with the mixture. Note that the keys are extremely porous and will absorb a lot. Try not to pass out from the fumes, it's a good idea to have eaten so you aren't more wobbly. Once all is painted, injected and dried, reassemble and remove drop sheet.
Leave loads of windows open for a few days, and repeat whole process in 6 months. Argh!!
Beware - you may dream of borers eating into you for a couple of nights, so be prepared for very broken sleep.
The borer oil is quite damaging to everything - the instructions repeat strongly that it must never come in contact with anything that may reach any waterways - that includes rubbish going to tips, or anything left in the yard. Disposal of implements and extra fluid is by taking everything to the local chemical disposal place. Rather potent stuff, I think, especially the fumes... *cough*