I used to dip the pistons on oil to lube up the rist pins and to make sure the pistons had oil when they went into the cylinders upon assembly. Then maybe 20 some years ago someone stated to use WD40 for quick ring break in , I never had a problem with ring break in with the oil bath but I have used the WD40 from then on as it was not as messy with no problems. I even spray some in the cylinders before the heads go on . My thinking is to keep the cylinders somewhat wet as most will not be fired right away.