welcome to the forum bro i will try to help on this. as for the pits being new that is true and due to the fact that each time you polish you remove a small amount of outer layer of metal. that said the blower housing is cast, this is a common problem with cast material. if the look you want is truly chrome then either polish it as good as you can get it and clear coat it with high gloss clear or plate it. otherwise if you dont feel like polishing it again you can fill the pits with high temp lab metal and powder it near chrome or super chrome and clear. this will give you a nice looking piece but is not chrome like or even polished as far as luster and glow.
here is an example of almost chrome powder
http://www.caswellplating.com/bbs/al...php?pic_id=527
and
http://www.caswellplating.com/bbs/al...php?pic_id=481
and here is near chrome examples.
http://www.caswellplating.com/bbs/al...php?pic_id=480
http://www.caswellplating.com/bbs/al...php?pic_id=480
hope this helps out some bro and best of luck. keep us posted on the results.