I emailed Swindon regarding a replacement, also noting a few aesthetic discrepancies that I'd picked up on, and was told that it would be replaced. After this, I decided to give my 'Star' one last run.... and the b****r decided to work perfectly. From other examples I've seen, the aesthetic problems are concurrent with both batches - so I've ended up retaining my example and have informed Swindon so. I feel awful for making it look like I'm messing them around, but at the end of the day, if the factory that Hornby contracts the work to would build the chassis right in the first place, we'd have none of these problems.
If the P2, K1 and J15 cause the same teething troubles, Hornby will lose another customer
The first bogie axle is off slightly, so perhaps I'll outsource my 10-spoke replacements. I'll shuffle off and start detailing 4003...