The absolute best stuff I've found is called glazing putty. its kinda like bondo in a tube. You can get it at Pep Boys for about $2.00 fill the hole, let dry, sand. It really is that easy. Good luck images/smiles//icon_smile.gif
Sometimes you have to open the deep pinholes up a bit to force in the spot putty /glaze.
Just spin a drill bit with your fingers on the hole to chamfer the edges a bit (sometimes a deep hole will only cap off with putty ,then the primer and paint solvents knock it loose while you're finishing it)
If you get a MEGA void ,you can make a little funnel out of paper ,like those pastery sock things they use to put icing on cakes.
Just curl up some paper into a cone shape, tape the seam shut and cut the very tip off (very tiny hole).
Load it up with your bondo or more resin (mixed with hardener of course!) then fold the back end shut and curl it up like a tube of tooth paste to make it ooze out ,then inject it in your nasty void.
Try to get it to force out all the air as it fills up and leave a bit of a crown to sand off when its done.
Just keep in mind ,some pieces are beyond fixing and it's easier to just re-cast another and chuck the bad one.
My expeirence has been CA for small pinholes because it doesnt shrink. and Evercoat Glazing putty for larger holes. Word of advice, on the larger holes and bubbles try to score the inside surface so the glazing putty will adhere.
This is the best stuff. They are the only brand I buy. Its smooth, consistant and sands beautifully.