need a passenger side manifold 4.5 cerb pls help ???

[fubar sounds]

hi , apparently on the left hand side manifold the throttle butterflies wont tighten sufficcently and i m backfiring whilst hot and idling , this only became apparent after i had her remapped and chipped , having lived with it for a while its annoyed me enough to get it sorted , i v had the offer of getting it rebored but thats a 6 hour job and the only people i would let do that will want roughly 600 quid so , a replacement would be much cheaper , anyone know of anything potentially available, thanks.