Chrome plating GSX750ES 1985 Exhaust manifold

[GSX750ES junky]

A few months ago I decided that since my exhaust pipes are chrome plated I might as well have the manifold chrome plated too.
Before the manifold was plated I had it sandblasted and thoroughly cleaned (see attached picture before manifold was plated).
After it was plated it sat sown in my garage for a few months covered with WD40, never outside and never exposed to the elements.
The problem started when 2 months after it was plated (while it was still in my garage) the manifold started showing heavy rust inside and later outside deep in the crevasses of the welding. Not a lot but still visible. What I did is to apply epoxy putty onto the corrosion , only to find that it comes out again from underneath the epoxy putty.
The person who plated the manifold told me he uses a 3 stage plating process: Copper , Nickel and chrome.
Could it be that he left residues of acid inside the manifold ?
How can one explain the fact that chrome coating soaked in engine oil starts to develop corrosion ? What would happen to it when it's exposed to the elements ?

[MadCapsule]

I would suspect that the WD-40 was actually the problem.

Check out posts 22 and 30 here.

You probably didn't need to do anything to protect the chrome if your exhaust was already being stored indoors.

Edit: Looking more closely at your picture, it looks like - don't take this the wrong way - that may have been a pretty bad chrome job to begin with. It may just be the picture, but the plating looks wavy and uneven, leading me to suspect that they may not have done proper prep work.

[GSX750ES junky]

I agree with you that WD40 marketed as anti rust material is nothing but a fraud. Nonetheless I sprayed WD40 on many other chrome parts including the whole of this 2 feet manifold and I can tell you that besides this specific area where there are hidden notches and welding all other surfaces (including this manifold) are shiny as a mirror.
What might be smoke that comes from the gun of the guy who did coating is the attached picture taken inside the manifold. Note the residues of what seems to be a cemented mix of rust and acid.

The picture in my opening post shows the manifold before the coating :-)
I'll take a picture of the external rust later today...

[GSX750ES junky]

Here is a picture of the manifold after it was coated. Arrow points to the external rust. One would say that the epoxy putty caused the rust but consider that I applied it after rust already started.