Posted: 14/08/2012 at 20:19
The second question is the one that shouldn't bother you. The blemish on the bottom of the fruit is called "cat facing". It's very common and has no impact at all on the fruit or its flavour. At worst you'll get some tough tissue around the edges of the blemish when you come to eat the tomato. Just slice it out. "Cat facing" has its source at pollination, usually as a result of low or fluctuating temperatures.
As to the first question, it does look like a stem rot. There are a couple of versions of it, the one I'm familiar with is a bacterial problem. I fear the plant is cactus, so to speak. Out of interest, when you pull the plant, have a close look at the roots and post a photo.
On the bright side, better the serious problem with the Sungold than the Black Russian. The BR is a much nicer tomato, IMHO.