[V8] Oil reccomendation?

[Daniel Hussey]

1993 V8 Quattro with 115K

The valve cover gaskets leak a little at the moment (need to replace these soon)...  Wondering what weight oil is reccomended here.  The manual really didn't say anything here.  The car hasn't been getting synthetic oil, so I really don't want to start using it now as I'm afraid this thing will leak like the Titanic.  

I'm probably going to run Castrol GTX...  Was planning to run a 10W40 weight oil, but someone on another list reccomended 15 weight oil.  Just wondering what others here are running with good results.  

I usually run a thinner oil, but in certain cars (like my Porsche 944S2), people all seem to reccomend a thicker weight oil.  I run 15W50 in it.  

Thanks,
Dan