After 29 years the steel nipple in the alloy head (below & between the inlet manifold "pipes" for cylinders 3 & 4) has bad surface corrosion in the area where the heater hose fits over the nipple so I need to replace it. I am concerned that the nipple may be "frozen" to the head by 29 years of corrosion of the thread even though there is no leak from the thread. Can I safely remove this nipple by using a hex spanner and a lot of force from a breaker bar (tube)slipped over the spanner shaft. Its easy to get to after removing the inlet manifold. The nipple appears very strong being made from 1/8" thick steel walls so I don't want to risk tearing the thread out of the alloy head. I could not find any aftermarket nipples on the web or is this likely to be a plumbing supply shop item?