I would predict the orginal engine will increasing add value. People are still taking orignal engines out so the supply of Series with orginal engines is still going down, soon an original engine series will be hard to find and values will rise at the same time there will be a shortage of engines. Following the price of 2 1/4 petrol engines on e-bay is informative. Good engines are £900 but very good are now £2500+.whereas the TDIs are around £500 with really good ones (ie with warrenty) still less than a decent petrol. I would grab a petrol off some fool who's taking it out and putting it on e-bay and doen't realise how it will be to get it back later.