I don’t claim to be a conservator, but I susoect that a conservator familiar with the problems of wood exposed to weather might suggest impregnating the wood with a fairly high molecular weight of polyethylete glycol (aka PEG). It’s essentially a water-soluble wax. You’d need to dis-assemble the bench (unless you can find a heated tank big enough to hold the bench in its fully-assembled state.)
There’s lots of information on PEG impregnation freely available online.
If the bench is presently painted or varnished, it would probably be necessary to femove that finish in order to allow the PEG to penetrate the wood.
It’s my guess, however, that this or any other treatment will do no more than buy time and reduce the rate of degradation. It won’t provide a permanent fix. Mean old Mother Nature will win in the end.
A siden effect of PDEG impregnation would be a waxy/greasy appearance and feel to the wood surface. Folks sitting on the treated bench might find their clothing stained.