Hoarding is either related to or is a quality of life strategy, which stems from the emphasis of a human need and forms the basis of a temperament; aside from being a very effective way to stockpile a sufficient diversity of resources to maximise ones freedom to build "almost anything". As a behaviour, it becomes dysfunctional in social environments which deny the individual sufficient space to store possessions or deny adequate access to knowledge, skills or tools necessary to turn parts and raw materials into something useful. The short answer for me, when stuck in this habit, was to decide what I wanted to build and let the necessary parts come to me in the fullness of time. I still wound up with a lot of junk but at least it was manageable enough to make use of. Ironically, this actually made it a lot easier to let go of stuff that was starting to get in the way because, as it turned out, the most vital raw material for any new project turned out to be work space!
I think you'll find that OCPD is a temperament-specific expression of solipsism. In the broader picture where typicality replaces normality (in terms of valid statistical modes), solipsism (as a family of temperament-specific disorders) is not a question of who you are but how you behave when you assume that your temperament is the only normal temperament (i.e. when you take on the assumption that who you are is the yardstick for "normality"). Of course, being the only person in the world who is "normal" or "right" or "sane" has it's perks, purposively speaking (and statistical absurdities aside). So convincing a person to give up a fundamental assumption that underpins their entire way of life can be a bit like trying to convince a true believer to give up their faith in something they really want to be true. Patting them on the head and telling them they've got a mental illness won't help either. They either use the gesture as an excuse to deny responsibility for their actions or they simply decide that you are the one who is insane, or both, depending on who they're talking to. Either way, their behavioural dysfunction is not corrected. And, because the closest physical process to fit the nature of the problem is cognitive, there isn't much chance of there being a pill for that either.
You can lead a man to reality, but you can't make him accept it.
The idealist/perfectionist variety of solipsists (i.e. typified by the DSM's description of OCPD) tend toward psychopathy not sociopathy (i.e. APD), although the APD criteria in the DSM-5 seem to encompass both sociopaths and psychopaths. So we have two ambiguous groupings with significant overlap which mirrors the same methodological problems in the MBTI. The problem with a lot of what you find in the DSM (especially the methodological mess made by the whole PD-TS approach) goes back to the same kinds of trait generalizations which make the classification systems of both James (philosophy) and Jung (psychology) just a tad ambiguous. The problem, regards Psychology, was that Jung put together his Personality Types in the absence of a rigorous purposive framework - which is why the MBTI (which is really Jung's Personality Types reloaded) makes so little sense beyond its application as a psychological mirror. Of course, one can hardly blame Jung for this any more than one can blame Napoleon for neglecting to call in an air strike at Waterloo. Purposivism, after all, came just a wee bit later with Tolman. Unfortunately, as with the refutation of lumuniferous aether, the profession failed to revisit numerous earlier assumptions in the light of dazzling new facts and, like Michelson and Morley before them, Tolman and Maslow failed to motivate the related professions to re-evaluate all of the ideas built on assumptions contrary to the facts that their research brought to light.
As Jean-Baptiste Alphonse Karr wrote in 1849, plus ?a change, plus c'est la même chose (loosely translating as: "The more things change, the more they stay the same")