Amazing bunch of replies - I do love this forum. Thanks everyone. here's an update and another confession...
First, just to clarify the whole situation (as per some of
@Glitch ‘s questions). We ordered the mower. It arrived with oil in the bottom of the box and around some of the outside of the machine. We queried it, especially in light of the fact it is supposed to be sent empty, and wondered whether it was a customer return (though there’s no other signs of use). They said – without any further ado – that they were going to refund it. Pleasantly shocked we were!
They haven’t sent a replacement, we’ve just got the one they refunded. And it isn’t a case of it not working; I haven’t actually tried to run it yet. I was concerned that trying to run it with oil in places oil shouldn’t be could cause problems. So I’m now on a mission to see where the oil has got to and to clean it up as needed (if needed).
The blade stuck thing was me being a complete silly billy – trying to turn it by hand with the brake on, and thinking it was stuck. Not my proudest moment. So that can be ignored (or laughed at).
Unfortunately, I think I’ve been similarly stupid with the “creamy oily filter”. Here’s what happened… When I checked the filer it was thick with oil. I’m guessing that a lot of the oil that escaped ended up there, and the sponge being a sponge soaked it up. It only turned creamy when I had it in a bucket of soapy water and was trying to clean it up. From what I’ve now read, oil does that in water!! This isn’t a wind up, I promise! I’ve got a lot of learning to do.
I agree that it is looking like the machine has been sideways, upside down, etc during transit, which has led to whatever amount of oil was in there getting to places it shouldn’t. It was sent from the Netherlands I think, so has probably been loaded and offloaded several times, and I doubt people have been bothered to keep it the right way up. Not that they would have needed to had it been shipped empty (which it was meant to be).
Because of work I've not been able to do as much as I had hoped on it. I've taken the spark plug out and it was clean on the inside but a little dirty on the outside. I've taken the engine cover off to look for signs of oil. And that's about it.
The mower is a Sprint 460P and is has B&S 450e engine. It is a push mower, not self-propelled. I don't think it has an oil drain point; you have to drain it from where you put the oil in.
Photos to follow.
It seems there are two main approaches, one to delve deeper and look where the oil has got to, and the other to drain it/pull the cord with SP remove whilst checking for oil in the SP socket (etc). Perhaps with the info above and the photos below it will be clearer what's best to do next.
Once again, thanks a million for the help, and for sticking with it even in light of my small engine faux pas!
PS - and thanks
@clogs for that kind offer, although I'm not sure they'd let me through airport security with the mower.