... I'm wondering if the Rocker covers purchased from Speedway were made under the same circumstances as the poor performing Offy  Tri- Power intake that Ted Eaton tested,  along with 6 others quite some time back?.. Long story short, the Intakes were not made by the original Fred Offenhauser's company, but by  a nephews company of the same  last name.  A law suite resulted. many years ago,  but  a Judges bad ruling in the case did not really resolve the issue.. Recently, an out fit in Canada popped up advertising new Offy parts.. So ??..

Paul

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Have these covers ever not leaked? are they new? Are they aftermarket, I don't know if there are any aftermarket T-bird valve covers. 
This may or may not help but I'm running a set of Offenhauser cast valve covers that I bought new from Speedway and they leaked, both of them. I checked the gasket surface and found it was not flat, I set them up in a mill and ran around the gasket area to make it flat and no more leak.   

I have had similar trouble. I took both (aluminum) valve covers off last week and checked the oil flow at idle. It was comforting to see a good flow at all rockers and out of the overflow tube. I installed neoprene Best Gaskets. RTV to the covers, gaskets taped into place and left to cure overnight. Then a small smear of non hardening goo to the other side. Tightened lightly, no leaks!

If the oil system is modified to increase the amount of oil to the top end of the engine, then the potential for the oil to be above the cylinder head valve cover rail is greatly increased.  I find it necessary to install restrictors with a 0.078” orifice at each rocker arm assembly to control the amount of oil that gets to the cylinder heads when making modifications to increase the oil flow around the center cam bearing.

Lorena, Texas (South of Waco)

Tim McMaster has a YouTube of an engine running with the rocker arm shaft overflow tubes blocked. It shows how much oil the drains in the heads to the valley can take. Sounds like something else is the cause…

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Hi Joe. I just took it apart again. Using a piece of Coat Hanger Wire I was able to get in about 7 inch's. Seemed very narrow about half way. Just big enough to get Coat hanger through. It was I think plugged up until I worked the Wire through. Is there a very tight Area normally? Feels like part of the Head Casting maybe. Going to go for a Drive later and see if there is Oil drip in AM. Thanks

  

Those end holes at both ends of the head go into the lifter valley if you have a long enough tool.  The holes are huge in terms of oil drain back area, and should be able to drain the area easily.  There could be an umbrella seal piece lodged deeper down where the head gasket mates to the block.  If you push it in, you will need to remove the intake, valley cover, and clean out the debris so that it doesn't clog the oil pick-up screen or worse get sucked into the oil pump and stop the rotors.  If you have a scribe with the 90* end you might be able to retrieve the blockage if that is the case.  Just some ideas.  Joe-JDC

JDC

Its just the One on the Left Side. Dripping down the side of the Head below the Cover..

  

It's odd that both covers are leaking. Is it possible they have pinholes in the casting ?
What is the head valve cover gasket surface like at the back edge ? is it rough ? missing some ? big bumps ?


1936 Ford 3W Coupe : 56 T-Bird 312, 47 Packard 3 speed, 40 juice brakes.
1968 Merc Cyclone FB GT 390, Getting a better front clip!
1977 Ford F-250 Supercab RWD Explorer Long box.
1976 Chev Camaro RS LT
Future rebuild : 1949 Ford F-1