Leaking Boiler Tubes are not necessarily a serious problem. However the reason for the leaks needs to be found and until this is known all is just speculation. For example; Expanding tubes into the tube plate is more art than science and is a delicate procedure, expand too much and the steel around the tube hole is hardened and distorted, not enough and it will leak. There are other causes for tube leaks but until more is known I would not jump to any conclusions.
As a general comment the boilers of locomotives in preservation are subjected to stresses from more frequent heating and cooling after each outing. In regular service the boiler was generally kept hot between runs. This led the CR to change the pattern from relay working on the Trans to servicing the locomotive at each depot meaning that the same locomotive did the entire trip and was kept hot for the whole time. This reduced boiler problems considerably. Of course, in preservation it is not practicable to keep a locomotive hot for a week or much longer before its next use. (On the NSWGR the turnarounds were generally only hours long, on the CR it was the next day or so).
You are correct in each case Neil, certainly it may be a small issue or more, given that 01 has not had a great deal of running following its RTS, and most with in many respects light loads even in the load trials, the boiler is pretty much in running in condition as far as the boiler is concerned, the aspect of how long prior to each run and after such runs is the loco in readiness as such with fire lit, and engine in steam, even light steam.
If one goes back to steam days & using Enfield as an example weekends generally had little steam working after noon on Saturday and until late night on Sundays. As early as Friday nights as engines came into the depot, the fires were dropped and not lit up until the Sunday afternoons & generally late afternoons. Once the program was put up on the board outside the chargemans office, and the shed crews, and fire lighters came in from 1400 the engines were readied and the light ups generally started around the 1700 mark or earlier depending on when needed. Usually 3 hours between the lighting up of the loco's was had to ensure they were ready for preperation another 1hour & then to the Whistle out point and water taken.
It was not uncommon to find engines with leaks in the fireboxes but fitters were there to ok them and in most cases as the boiler heated up and steam was raised, the leaks disappeared as the heat increases had the respective issue fixed by heat expansion, not always though, and in bad cases it was seen by how much water was showing in the gauge glasses, when stabling the were required to be at least 3/4 full in the glass.