update for reference.....
the decking oil has done its job well, its going to be the sheds 3rd year this year, just starting to peel and look a little patchy on the front ledge/cladding where it gets the brunt of the sun/rain, so we're going to coat it completely this year again.
everywhere else looks spot on still, its tempting to leave that and just re-do the peely bits, but i think it makes sense to do the job properly.
used liberon decking oil all over first time round and it was a good call, its worked well. also used 4 tins, which comes out around £200 now.
had a look on the DIY forums and barrettine clear all in one decking oil seems to be well recommended, and half the price, so going to go with that this year i think.
https://www.toolstation.com/barrettine-all-in-one-decking-oil-treatment/p25816?bvstate=pg:2/ct:r
You may find you need a lot less when reapplying as it won't soak in as much.
ok, im sure they wont run out of the stuff if i only buy a couple to start with, thanks.