My Pentax ME shows the wrong focus in the viewfinder. Is there any hopes of repairing it myself?

How I've confirmed it's a viewfinder focus misalignment issue:
I take my manual-focus lens that focuses up to infinity (not beyond) and it focuses perfectly to infinity on my Pentax DLSR. The same lens is showing off-focus in the viewfinder of my SLR. Meanwhile, several photos I've taken on my SLR have been off-focus (by a wide enough margin that user error is unlikely). This holds true for several lenses, so it seems likely that the SLR is focusing fine, and that the viewfinder is simply showing a wrong focus setting.

I've heard this may be caused by either a misaligned focus screen, mirror alignment problems. Are those easy to fix? I could use the DSLR to validate that the viewfinder focus is accurate to avoid having to shoot an entire roll every time for confirmation.

Any help would be greatly appreciated!