[British-cars] MG TD oil leak

[Mike Duvall]

My MG TD had the typical drip when you shut if off but recently the  
puddle has grown quite large.   It is dripping when I drive and it  
rolls out pretty good when you shut it off resulting in an 18" spill  
underneath after the puddle soaks in.   I am somewhat concerned that  
it suddenly is leaking more than before.

Should I be using 30 weight oil instead of a multiweight?  Could  
lightweight oil drip worse than thicker oil?  What would cause a  
change?  There is a pretty good layer of gray form-a-gasket on the  
pan with only a few thousand miles since a rebuild.

Any suggestions?