Yes, I think it should have two steel balls. I did have a thread on trying to repair one but MB must have a special jig which compresses the balls and then allows the piece to be slid into place. It seemed virtually impossible to do this without such a jig.
However, in my case, I think that the grease around the ball(s) had hardened and had I simply removed the part and sprayed WD40 into the holes where the balls seat, they would have freed up and the part would have been functional again. It is very hard to get lubricant on the balls with the part in the door, but it is not impossible with an aerosol can and a plastic extender hose.
I think the popping noise is indicative of a stuck ball. Do not ignore such sounds. The check strap can freeze in the open position and it then has to be removed in order to close the door. This happened to me at the most inopportune time.

Don't take the new one apart. You won't be able to reassemble it.


Repeat the mantra: Check your balls and keep them lubricated.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13