Apparently, getting the rubber bushings to press in often causes
shop rage . .. .loudly muttered split infinitives, tools in high velocity thru the air. . . tramatic flashbacks to the first discovery that "made in China" condoms are NOT going to work.
Okay, seriously . .. Roland, wayback, pointed out that Porsche was concerned about keeping the bushings sealed tightly. (apparently roads have dirt and grit on them sometimes -Capt Obvious)
So, I see two ways to seal these. One, chemically bond; two, physically constrain. For various reasons, I believe that Porsche chose to physically constrain these.
Now, just because they go on "pressed" does not mean that no bonding takes place. It's a funny thing, adhesion . .. ya press a piece of rubber against a piece of clean steel for 10 or 20 years, and guess what?
Of note; the very old a-arm I have to play with is fairly concentric (read: no 20years of loading) .... the bushing will stick to the center shaft for ~15° of rotation. It then breaks loose, and drags, slowly, smoothly, arounfd the center.
I believe this slipping to be part of the genius of the design. YMMV