Mamiya 1000DTL focussing screen tune-up

I have a Mamiya 1000DTl from the 60's which I still use and works good,though the meter is long since gone. The focussing screen is very dirty and there is the red shadow on the bottom. i would like to find someone who could either replace the screen and perhaps install an Accumat type fresnel lens to brighten the image, or just give it a cleaning.