you just lost the top plastic wing-nut and the metal cover, i dont believe it exploded, maybe just shook itself loose and fell off,(if it did explode of from there, the metal nut inside the wingnut would stay on there).

you can definitely do it yourself, just go pick up the 2 parts you are missing, check the filter to make sure nothing big fell in there, top up with PS fluid and cover it up.

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1987 300D W124.133