I’ve had two previous trips to the GZ to look for this cache: turns out that the hint in the Wherigo cartridge is completely inaccurate and mislead me quite a bit! To reiterate what others have said (I should’ve looked at the past logs sooner!), you’re looking for the kind of thing you’d normally expect to find given the cache size and location, NOT a combination lock.
Enjoyed the Oxford tour but ending on the edge of an industrial estate-turned-building site puts a dampener on the whole experience! Perhaps this final stage could enjoy being moved elsewhere? It’s possible it’ll have to anyway, once construction is complete here.