Villa - Here is an answer from another post from (Rodney) about WD40 and why it isn't good to use. There may be more than one reason, but here is at least one good one:
(Rodney)
Do not use WD40 for long term storage. If you use it for cleanup or anything, rinse it out well with a good oil. Never use it in an older engine unless you want to agravate the wear as, any rust already present will be turned into a nice abraisive compound to accelerate the wear of the engine the next time you use it.
So apparently the WD40 will loosen up already rusted areas and cause undesired wear.