Funny you should mention that I think it's the one thing that's gone wrong. I've just put fresh oil in and a new filter and started the car up for the first time. Engine didn't explode so the timing must be OK, but I think I now have a new oil leak from the sump in a different place and worse than before. I can't be sure though as it's right under the filter and taking that off spilled a lot of oil down the front of the block, so I'm gonna leave it overnight and see how much has leaked tomorrow.
Actually getting the sump off and back on isn't that hard. It's easier if you have the bumper off so you can drop the radiator subframe mount and the subframe brace, but i think it would be doable without doing that. You ideally need a 1/4 drive torque wrench, E8 star socket, and some 1/4 inch extension bars, some of the bolts are really deep inside a long tube (gearbox end, 4 of them). As for stopping it leaking, well I think I should have bit the bullet and got a new rubber gasket and not bothered with the red RTV silicone. I don't think you can really do it with Silicone alone as the gasket sits in a recessed channel (you can see in my pics) it's not two flat pieces of metal butting up against each other so you'd need to fill that channel with silicone and you'd need loads. The hardest bit is keeping the mounting face of the engine block clean while you fit the sump with new gasket because there's constantly oil running down from inside the crank case.