Done it before, you might get away without tax but that is rare. There is a way round it and it's long winded, you have to go through The Republic of Ireland. Anyway, the simple way is be prepared to pay VAT on it when it gets here. If you can speak with the seller get them to put a reduce value on the package the only problem with that is if it went missing you would loose out when the insurance payout. For the item description tell them to put "replacement parts" not New Item
Hope it gets delivered by UPS or Parcel Force. UPS best bet to get away without paying VAT. No import tax or license needed.
You do get some bargain off ebay from those yanks Try ebay.com instead of ebay.co.uk ask the seller if they would ship to the UK. Look out for the ones that say "make an offer" then do like I did, made sure i got a deal.
Happy bargain hunting!