TOPIC:

It really doesn't matter which "brand" you use but what is critical is ensuring that whichever oil you do choose, it's JASO MA certified. This standard was specifically put in place to certify oils that can be used in motorcycles with a common lubricating system where the clutch pack is also included in the engine oil circuit.

My personal favourite is Shell Rotella T6, a fully synthetic motor oil available in 5W40, 15W40. I've used this in my Ford F350 turbo diesel pulling a 14,000 lb trailer, in both of my F150 ecoboost and Lincoln MKX and all of my power equipment. I love the stuff. And it prices out at around $38.00 a gallon Canadian.

I've scoured every document I can think of to get an explanation on what's under that cap plug. It's definitely on the main oil gallery feeding the crank main bearings, but it's unusual for it to be there. There's no production reason to put it there, but it is a relatively large cap which could have been accomplished with just a plug. there's nothing in the service manual discussing the plug. All of the pics on Ebay showing different views of the lower half crankcase don't reveal any notable information. It definitely does not protrude into the crankcase under the #4 crankshaft journal so it's on the main oil feed gallery.
I'm tempted to pull the "cap" off of mine just to confirm it's "just a cap" and not access to something like a check valve. I have to pull the engine on my bike to do the primary and secondary chains and I'll be going over the entire engine internals while I have it all apart.

I'm with Pete on the oil viscosity, I'd recommend 10W-40 for the British climate. I'd maybe go to 20W-50 in a hotter climate. +1 on the Halfords semi-synth motorcycle too.
Are you sure it's not weeping from higher up on the front of the engine? It's not unknown for the water pump oil seal to go & this usually announces itself by an oil weep from the water pump drain hole (which has owners thinking it's a base gasket oil leak).

I agree with that cap being on the oil feed side. A theory: The engineers may have originally had a second feed designed into the castings and for what-ever reason decided not to use two, but rather just the one existing feed. It would have been too costly to modify the casting mold to remove the "boss" so they simply tooled/threaded it to accept this cap/plug. The cap/plug flange is thick enough to have an o-ring incorporated and I would not be surprised to find one despite there being no reason for this cap's removal. Perhaps the o-ring (if fitted) has shrunk with age thus causing the weep. If there's no o-ring then what ever sealant was used has apparently deteriorated enough to cause the weep. If an o-ring was used then the cap/plug should loosen "relatively" easily. If a thread sealant was used - that might be a completely different story. Either way, any attempt to remove it should be attempted with a socket.

Just looked at my A5 and it has a sunk in grub screw type fitted with an Allen head, strange that they redesigned it later..maybe to stop oil leaks ?

Would it be to attach an oil pressure gauge for testing purposes?

BTW I've been using shell helix ultra car oil 5/40 on my zzr 600 for years and now on my triumph 955 and z13 and NEVER had clutch slip, having said that now bit concerned if it's up to the job of lubing the primary/secondary chains after previous post on this subject,,