Looks like a Nakajima Brother to me. Indeed, very reliable, light and a delight to type on! (:Check the serial number under TW-DB's Brother category. I's guess mid-70's.
I've got the very same one - sheet metal, sticking keys (the - and something else on the far right - what did you do against them on yours?) and unknown age, but as I wrote in my Collection entry, Robert Messenger had a post about them, according to which they're around 1971.
Mas - Those were the sticking keys on this one as well. I just used a tiny bit of 3-in-1 oil in the segment (I've heard this is a no-no but it seems to work for me) and then worked the typebar back and forth for a while. It only took a minute or so before it was working properly again.
It is a Silver Seiko I believe, and yes quite excellent.