The Medway Handyman wrote:
As long as you are sure its never been treated I'd agree with Pete C.
Decking oil soaks in rather than forming a surface coating, so it's easier
to apply & top up. I'd avoid any kind of seal, epoxy or not.

I've used clear decking oil from the sheds & found it OK.

Dave, thanks for the advice. The idea of using something that sinks
into the wood, rather than just forming a film on top of it, as paint
does, seems like very good sense to me. However, I have seen quite a
lot of references on internet pages to how algae & suchlike love to
"eat" oil-based treatments, i.e. people claim that the organic nature of
the oil while soaking into the wood is also attractive to the green
stuff ! Have you used oil-based treatments and not found this to be
the case?

Eddy.