Not huge amounts, but if it's a guard depot it needs full secure facilities for taking in and paying out cash, plus suitable space for management, breaks, lockers and anything else. As it happens, drivers at Piccadilly CAN book on at Stockport if their job starts at Stockport sidings; guards can't as they need to collect their equipment and cash.
So, as far as drivers are concerned, Stockport is a traincrew depot in all but name..
I have no idea why diagrams place stock in certain locations - I only drive it there - but Stockport cannot do anything beyond topping up some fluids (oil, water, sand), cleaning and emptying toilet tanks. I don't know what the maintenance schedule for a 323 is, however every time one is on Longsight it receives a full check-over and any faults raised can be rectified. Ditto diesels which overnight away from Newton Heath.
So what would be likely to be checked on a 323 stabled at Longsight which wouldn't get checked at Stockport, without actually taking the unit into the workshop? Or are you saying that any 323 arriving at Longsight is automatically sent into the workshop for a check, even though there would be a 50/50 chance that it would have received the same check only the night before?
Stockport probably has some additional space, but not huge amounts.
I estimate that, as things stand, Stockport could accommodate approximately 50% more stock than it actually does. That does assume, however, that any stock arriving is going to be in a 2-car, 3-car, or 4-car formation. If Stockport were to become restricted to 3-car and 4-car EMUs, that would reduce total capacity, but still to more than is currently used.
It isn't a depot in effect; just some sidings - no different to any other unit stabled out on the network (Buxton, Wigan etc); it just happens to be larger.
Stockport might be bigger as a whole than Buxton or Wigan, but the latter two do accommodate more diesels. I'm more critical of Buxton and Wigan being devoid of fuel than I am of Stockport. The lack of fuel at Stockport is a problem easily solved - simply transfer the diesels away. This is something which would be possible now, but will no doubt be made a whole lot easier when the Manchester (Picc)-Bolton-Preston route goes electric, and four train duties (approx) which are currently supplied from bases in the Manchester area, change to electric as a consequence.
I've worked for a bus company where any vehicle returning to depot would have its tank topped up, even if it had only been out for only half an hour or so. I've also worked for coach companies with just three or four coaches, but which had their own fuel facilities, nevertheless. The situation of a DMU being refuelled only every second or third day (or whenever) seems to be taking unnecessary risks, although I have to say that the system seems to work, as I've not heard of a DMU actually running out.
Would diesel be misappropriated if it were available at smaller bases?