Originally Posted by MichaelW

Once every few years does it for me.
MKS pedals are typical platforms and can be stripped for cleaning.
You need to remove the end cap, this is usually plastic. The flat ones prise out , the domed ones unscrew. I use a pipe wrench but handle with extreme care or you crack the plastic. The plastic "seal" on the crank end just prises out but again, try not to cut or damage it.
I adjust and hold the cone with needle-nosed pliers and use a small wrench on the locknut. There is an anti-rotation washer between but it wont stop the cone from turning a smidgeon during assembly.
You often get a hard residue on the bearings from decomposing grease. Just clean and scrub in solvent and rebuild with plenty of waterproof grease. I reuse the ball bearings.