2001 with 326,000+

Previous sloppy work as VP44 had 2 top studs with nuts & rear bracket was broken. So I’m assuming original pump went out prior to 127,000 mi when I bought it. 
Over the last year, oil leak developed. I wasn’t overly concerned with miles upwards if 300,000 until I was adding 2 to 3 qts every 100 miles or so. Eventually traced the leak to either vacuum pump or pushrod cover. Resealed pump & replaced power steering pump. Still had the leak. 
Pulled the VP, Vacuum pump & the cover.  Replaced the seal on the cover. Inside of 2 weeks the new rubber seal blew out again. 
I will use a high temp gasket sealant this time AND ADD aluminum flat bar the width of the cover so I can increase the pressure applied by the bolts to the outer edge of the cover. Longer bolts to accommodate the 1/4” flat bar. 
Also will drill holes & thread them 1/2” from ends of flat bar to add vertical pressure along edge of cover if needed. 
I will add pictures when completed. 

 

Are you sure you're not getting crankcase pressure, I'd be checking the breather 

 

While running and warm take the filler cap off if it blows it off like a missile check breather

Picture of flat bar tensioner on outer edge of cover. 

Update: When I checked my cover it had about 1/8” bow or warp along the edge. 
I installed 2  51/2” X 1 1/4” flat bar tensioners to exert pressure to the outer edge of the cover. I also used a high temp JB Weld silicone sealer to hold the gasket in place with this repair. I pulled the bolts much tighter than specs.

Got it back together at dark yesterday so now to test it. 
I do have some blow by but I cleaned the breather when I first replaced the gasket. 
 

I do not use sealant anywhere OE didn't use sealants. I would of considered replacing the tappet cover with a 12 valve tappet cover. This way you ditch the crappy stock crankcase vent in front.

Update: Almost a month now and no leaks!

 

First time I did repair used RTV with Cummins gasket, was getting headlamp dark in drive way by finish time. Within 5k was leaking horrendous again.

 

On second repair found the RTV had assisted in gasket slipping out and getting pinched during torque. This one has over 100k no issues.

Yup. Why I normal don't use any sealants where gaskets or seals were installed with silicone. The only place I know where silicone is used on the entire truck...

 

Front and rear differential covers

Transfer case halves.

Gear case cover.

 

Those places I use grey RTV. No issues I'm at 444k miles and no leaks currently maybe the oil pan gasket.

I use a Cat sealer that is no longer sold, luckily I have a good sized tub of it, it's really sticky and comes with a brush in the lid of the cap, you can just paint a smear on no problem 

 

This is smeared on and pretty much left to go really tacky then the parts bolted together but not torqued just nipped, torque after it's dried, works every time and seals some right poor surfaces

I just recently did a 810cc twin engine in a 1963 Howard rotovator, made a base gasket for the barrels but no headgasket, intake or exhaust gaskets, reused and this stuff sealed everything no problem H/G was copper though

Gaskets tend to squish out using sealer if torqued straight away but the Cat stuff I have seems to grab the gaskets better and faster and unusually it only really sticks to the gasket if stripped again and not the part