Just to close the loop on this...
I finally opened up the SK1-73 today (it does NOT match the SK1 Service Manual diagrams that I have wrt removing the Top Cover - small "L" bracket vs two "L" channels) and discovered that it actually was the low-F key that had that small plastic piece broken off from it (pics attached). The "ting" sound on the C6 key (that I though was the problem key) was just something funny with the return spring and after I reseated the C6 spring the "ting" went away.
Hammond Tech Support and Hammond Central were both very helpful in locating a replacement key, but in the end, since it's the low-F on the keyboard (and it looked like I might have to remove the keybed to pop-out the key), I decided to just leave the low-F key as it is (it produces sound ok).
Anyways, thanks for all the replies.
SK1-Disassembly-Top-Cover.pdf