IMO, and these are all just opinions btw, I would run some MMO. I ran atf in my oil eating corolla but I actually ran it for a few hundred miles. That sludge isn't going to dissolve in 10 minutes in my opinion. Maybe a little but if it isn't really a problem, why do the more drastic measures?

 

And for the "contrarian" point of view: Is it "broke"? What are the symptoms? Noisy? Poor gas mileage? Smokes? Fails emission testing? Hard starting? Rough running? yadyadyada....
If no symptoms; it ain't broke! If it ain't broke, what's the benefit of screwin' with it?
Now maybe there are sludge deposits waiting to be loosened. What happens to them then? To get filtered out they have to go through the oil pump. Just a thought...sure, you want to start doing regular service to prevent further buildup, but trying to undo the past service record is pointless.

 

The problem with that much sludge is that it probably is clogging some oil passages, which can starve moving parts of oil - obviously not a good thing.

On the downside, some of that sludge may be plugging gaps around oil seals or gaskets, and when gone, you may find yourself with some leaks.

But with that much sludge, I think you pretty much have to try to clean it out, and hope for the best, leaks-wise. You may have to replace some seals or gaskets.

The ATF and other products mentioned will be a good start. To finish the job, use a group IV or V synthetic oil like Amsoil or Red Line for the next couple oil changes. Red Line in particular, being an ester-based product, will really clean the motor out.

 

Ran a quart of ATF and castroil high mileage in my truck for about 1000 miles.
Pulled the valve cover this summer, it looked brand new.

 

x2 i was going to ask this.
if you go ahead and do the flush, i would put a new larger filter on before just so you know its collecting as much of the crap as possible.

 

What kind of oil are you using that you've got sludge build up? And how long for your oil change intervals?

I got my truck at 100k miles, it's got about 187k on it now. There is no sludge. I've been running good synthetic in it since I got it. Why not try running a good synthetic through the motor first, rather than thinning you oil with something that could lead to rod/main bearing failure and cam scoring?

And what makes you think there's sludge?