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I just found on this website the answer to my question on 528 vs. 528T vs. 528 MPK.
http://www.terrylove.com/forums/showthread.php?40905-Korky-Quietfill-Max-Performance-Valve-528MPK.
I would also...

Terry, Thank you for the reply.
Unfortunately the problem is not with the water inlet screen.

For the replacement, should I use the suggested 528MPK model?
Home Depot only carries the white top...

This is an excellent website with good information. Others have asked for the instruction manual for TSU18A (lower photo), but Terry provided a link for an instruction manual to the one in the upper...