[Vwdiesel] '84 Diesel Rabbit Motor Oil 15W-40, 10W-40, 5W-40 . . .

[Bryan K. Walton]

Hi guys,
	So I've got an '84 Rabbit with about 122K miles on it. I've
been running Cenex Superlube TMS motor oil in it (15W-40 weight).  But
I thinking of switching over to a full synthetic oil.  My reasons for
considering this are:

1. Extending my oil change interval (I've been doing it every 3000
	miles).
2. To see if I can lower my oil consumption (I've already installed a valve
	cover baffle.  Right now my consumption is about a quart every 1000
	miles.)
3. To see, first hand, whether I can boost my mpg with synthetic oil.
	I know many synthetic oil users claim to have seen a mpg
	increase.  I'm a mpg geek, so if I can squeeze out even another
	1 mpg, it would be cool in my book. 
4. I only put about 6000-7500 miles on my rabbit a year. So, I think I
could get away with an annual oil change with a synthetic. I live in 
southeastern Iowa.  When I first started considering this switch to a
synthetic, I thought that a fully synthetic 15W-40 might work better
in the winter than a dyno-based 15W-40.

However, when I started looking for fully synthetic 15W-40s, I didn't
find very many:

a)Amsoil
b)Redline
c)Royal Purple
d)Neo

So, I posted a question on the bobistheoilguy.com forum to see what
people thought of these various options (they are all much more
expensive than the dyno options -- but cost is probably one of the
least important concerns of mine).  But I was unprepared for the
response I got:

"Any of the listed oils will do you fine in your Rabbit. However, even
though your manual states the use of 15w-40, it was published before
widescale availability of synthetic 5w-40 heavy duty engine oils,
which would be more than great for your little Rabbit.
You see, a 5w-40 synthetic oil will provide better cold weather flow
properties, and will also protect better than conventional 15w-40s at
high temperatures. It's the best of both worlds!"

I hadn't even thought about using a 5W-40 before reading this reply. 
So, my question to you guys: is anybody running 5W-40 in their diesel
A1?  Is there any reason why I should stick to 15W-40?  Or is this
poster correct, that 5W-40 is beats the 15W-40 in every fashion?

Thanks!
Bryan Walton