not sure baout car parts but ive ordered all sorts of other items from litteraly all over the globe , japan , USA , and europe and this is what i ahve come to conclude ...
pretty mucheverytime my items came via the airfreight super fast stuff (under a week from tokyo) i got stung for customs and gernally parcelfarce did the uk side and gipped for theyre "handling fee"
when i came via slow up to 2 weeks mail ...... no charge !
after getting miffted at the parcelfarce depot ( its 5 mins from house and i didnt want wit extra days fro them to send me a ltter then deliver the item ) guy i asked why do i somtimes get stung fro vat on the order some time but not other (same supplier) i was told "the world pack air freight stuff gets checked by customs almost all the time , but they hardly bother with the slow stuff ".
so if you dont mind a little wating whihc i dont on big orders then try and get its sent el cheapo post with insureance , might be lucky and get it sans tax.