I've also been building a Sealion ballast hopper using the kit from PRMRP, mainly etched brass with a few white metal castings.
I must admit I encountered a number of issues with the kit mainly due to inaccuracies in the etchings. Whilst the basic body parts went together OK the problems started when adding the detail.
Generally the etched holes for locating wire handrails etc were way oversize for the wire to be used but the main problem here were the holes in the bufferbeam for the shank on the white metal buffers to locate in, which were so oversize, parts of the holes were still visible after the buffers had been installed. Also the etch used to locate the hopper door operating wheels was such that when used as supplied the operating wheels were far too low so it had to be removed, modified (shortened) and refitted. I think the wheels are still a mm or so too low but I couldn't face taking everything off again! Then just when I thought I'd got to the last job, attaching the bogies, I found that the cross shaft between the handbrake operating wheels at the end of the wagon fouled the outer bogie wheels to such an extent that the wheels wouldn't turn never mind any thought of the bogie rotating. So again the bogies had to be removed, stripped down and modified to move them 2mm inboard, hopefully the photo below will show this. One advantage of this modification meant that I could reduce the size of the hole for the bogie retaining screw which like the other holes mentioned above was way oversize and allowed the bogie to move forwards/backwards and side to side as it wished! Note this new hole was drilled after the photo was taken.
Fortunately I had gone against PRMRP's instructions when assembling the bogies by screwing them together instead of gluing/soldering them so dismantling wasn't a problem. I also shortened the bolster by a couple of mm as I felt the bogies were too wide overall and this helped to reduce the excessive amount of sideways slop of the axles.
All of this was a shame, as overall I feel the kit captures the look of the prototype really well, the use of etched brass for the body being a great advantage over thicker resin or plastic alternatives. I suppose in many ways it just shows the age of the kit/etchings. Certainly it came as a bit of a reality check after recently building (in 4mm scale) a couple of the Penbits sprung loco bogie kits. The etches in these kits were the best I've ever come across, it almost "clipped" together. Maybe PRMRP should see if Ian Penberth could redo the artwork for the etches!
Anyway a few photos of the completed model (awaiting painting).