VITRA EA 124 loose metal base  

I recently purchased an EA124 from 1988 (Vitra):

Overall it's in good condition, however the 4-legged metal base detaches when lifting the seat. The tilting mechanism works just fine, it's only missing the plastic cover. Only problem is that for some reason the metal rod that goes into the tilting mechanism cannot be fixed permanently.. I don't see any shafts to keep it in place either.

Would anyone be able to advise me on how to get the base properly fixed to the tilting mechanism?
<img class="wpforoimg" src=" http://d1t1u890k7d3ys.cloudfront.net/cdn/farfuture/mk_MfN_3jGnqg9bjvCX_qP