Two topics: Channel 11 pixelation; PeninsularMark's antenna.
I recorded the I-Heart Awards Show Sunday night OTA from KNTV and watched it tonight. There is definitely a problem with intermittent pixelation on KNTV 11. It would occur frequently for a minute or two, then disappear for a while and then return. Being a music program, it was quite irritating when it was happening. I get a signal of 30 dB SNR (98% on the signal meter) from them (Mt. San Bruno is just 5 miles away), so there should be no reason for pixelation. There's either something interfering with their signal, or they are having transmitter problems.
Now to Mark's antenna... I agree with 888CallFCC that your problem is probably due to a failed part or your coax is going bad or whatever. I agree with you that after 40 years, it's time to replace that old antenna. Don't waste your time trying to fix something that old. I would order the Winegard HD7694P that Chuck recommended and replace the old antenna with this new one using all new RG6 coax. It's a good VHF/UHF antenna that will work great for you. You can have one in a few days from Solid Signal. This long URL will take you right to their page for this antenna: http://www.solidsignal.com/pview.asp...0Antennas&sku=
(Click or copy and paste the entire thing from the http to the sku=) You can also get the coax from them.
As for the distribution amp vs the 4-way splitter... the amp doesn't give you any loss while the splitter cuts down on the signal quite a bit. With a distribution amp you'd have more signal to work with, but seeing the splitter has been working fine, I'd just leave it. Just replace the antenna and the coax to the splitter and you should be in good shape.
Good luck with your new installation!
Edit: In your post that you made while I was typing this, you mentioned a possible rotor. It all depends on how well the stations from the hills above Fremont come in (1, 14, 36, 48, 54) with the 7694 pointed northwest, and whether or not you want any of the stray stations that are in other directions. The majority of the stations are all in one direction from your home. Look at your TVFool report to see what's available. You've got lots of stations in the green area!