Toyota Repair: EGR modulator on 1999 RAV4, toyota dealership, modulator

Question
I took my 1999 RAV4 into a repair place to see why the check engine light was on. He checked it out and said it was the egr modulator. ( the black saucer shaped item on the top back of the motor)It had a malfunction 401 code. I paid the $174.98 for replacement of the unit and the check engine light fee. I drove it around 50 or so miles and the check engine light came on again. I took it back to the same place and asked him what the deal was. He said it was probably crud buildup in the lines and he could clean them out for me for $50 to $60 dollars. While I was there this time I went back and spoke with the mechanic that had worked on it before. He showed me my old part and popped it open to show me the wad of white filter inside saying it was the dirty and the reason for the code. It did not look dirty to me, and the pads of white filter looked ok also but he was the expert. So he cleaned the lines, reset the check engine 401 code charged me $75 and sent me on my way. 20 miles later the check engine light pops on again. This time I took it to the toyota dealership in town and had them check it. It was the same 401 code as before. The tech told me it was a switching valve beyond that egr modulator way in back and below and tough to get at. He sprayed something to lube the part to try and keep the valves from sticking. He said the part was bad and the spray more than likely would not last. He was right, the light came back on after about a hundred miles but now is intermittent. He said in the 20 some years as a mechanic he has never seen a egr modulator like the one the other garage replaced go bad. He said on a 401 code he goes to that part he lubed first and it normally is the problem.  I went back to the first place I took it and told him I wanted my money back minus the charge for the check engine light fee. He refused and said the only way to eliminate the chance it was the egr modulator was to replace it first and go on down the line from there. The Toyota mechanic disagreed and said they could have figured it out without replacing the modulator. Finally, after alot of back and forth,they offered to put on my old egr that the mechanic had popped open to show me the insides and refund me "some" of my money. The mechanic that broke it open told me that once that part is opened it is no good. The owner of the place said his mechanic is wrong and it would work just fine. Would putting that old part back on cause me any problems?
Thanks for your advice.

Answer
It doesn't sound like the modulator valve was the problem, it can be checked easily using a vacuum guage and vacuum pump, there's no trial and error, good guess but wrong. The toyota mechanic was right in that the EGR vacuum switching valve is the probable cause as these are a common failure, so I think you should have it replaced and make sure none of the hoses are leaking.