The pen is still working. Some drawings from the past three days:
No re-fill so far as there is still ink sloshing around inside. No drying out, but the brush does act slightly differently after days saturated in the ink. There is more of the dry brush effect going on from time to time, and I can't quite predict what makes it happen - apart from rapid sketching. It might in part be due to the reservoir being low in ink.
Perhaps a re-fill and some carrying the brush around in my bag is due - taking the trials to the next level, and checking how the pen holds up to leakage and drying when treated a bit more roughly. To safeguard my bag and contents I will have to keep it in a sealed plastic bag until I am sure it won't leak, so that might influence the rate of drying.