This is interesting because my big Thinbar had exactly the same lesion a while back. It kept growing and looked like a small volcano in the end. I did the usual Melafix (sorry but I think its overrated and appears to be the cure to everything it seems) and salt but it did nothing.
In the end I took a risk and got hold of a fine (25G) sterile hyperdermic needle from work, lanced and aspirated it. It disappeared immediately and I was meticulous on WC and hygiene in the tank for a while (well-more than usual if you see what I mean). The Thinbar was perfectly fine and there wasn't a mark in sight-not had it since.
People might think I was mad but I lost a NGT to exactly the same thing in the past and thats when I tried the Melafix and all. With the Thinbar I thought sod it and decided to lance/aspirate it because I knew it'd go the same way as the NGT.
Hope this helps-honest to God your Pulcher has the very same lesion as my Thinbar had-was amazed when I saw your link