I haven't come across any special precautions for removal but there are warnings (in common with your 2445) about not operating the scope with the case removed unless you use an external fan to cool the hybrids on the main board.
Compared with prices in the UK, under $100 for a 2465B is a bargain. Mine was sold as not working and with no display, the usual corrosion from the electrolytics on the A5 board commonly makes the DAC reference voltage go way out of spec and this affects many sub-systems, trigger levels, beam vertical offset, brightness and probably many more. If 'yours' is suffering from a modest DAC drift it will almost certainly make it impossible to calibrate the scope. Mine had almost destroyed one of the thin film precision 10k resistors and had caused the beam to be invisible (and off screen anyway).
If you have a 2445 to do the swap and test of U400 then you do not need to commit any further money until you are sure that U400 is the culprit. Replacing the resistors and capacitors on the A5 board is well documented and, at least in my case, not at all costly.
Best of luck,
Roger
