Not really gun specific, but the "most difficult" thing that I have run into, on a pcp, was removing Ninja Regulators from their bottles. PCP airguns, once gased-down, can be complex and tedious, and that goes away with knowledge and repetition, but dealing with a long compressed spring of an FWB124 is always there. PCP are easy to work on comparatively, and require less space to do so. If you have space and a workshop, the problems become far less.