I have not removed all the vacuum lines yet on the 603 like Dave has done. Right now I have just removed the line to the valve and plugged the supply.

I agree with you. If you are selling parts to other forum members, you have an obligation to ensure their satisfaction. If the part does not fulfill their expectations, then you take it back, no questions asked.

My kits are offered under the same terms. The community of the forum is much more important than the petty cost of a part.