I can offer what I have tried on the three 2.5's I have - all with previous valve cover leaks...many others have been through this:
On the 2.5, the EGR valve must be removed (13mm U-joint socket) to gain easy access to one of the bolts.
I feel that the cover is VERY pooly designed, the clamps out there sound like a real good idea if you kind find them. I have seen bolts work loose if not "lock-tightened" with the removable formula.
From: Lance Osborne
"No matter what I do, my valve cover leaks oil. I've tried replacing the gasket, using RTV, etc, and they all leak."
I had the same problem on an 87 4-cyl., and no matter what I did, nothing helped (incl. RTV) until I got a cast aluminum valve cover from The Fiero Store. The flange on the flimsy stamped steel cover just gets bent too easily, so you can't apply enough pressure on the gasket, which would be especially important if the sealing surface on the head is poorly machined, like it is on mine.
The bolts aren't supposed to be tightened very tight, but finger tight is a little bit too loose. Screwdriver-tight works for me with the cast aluminum cover but that may be already too much for the steel cover.
From: Jukka Alve
I used a product called "The Right Stuff", to replace the valve cover gasket on my 4-cyl engine. I must say it does a tremendous job. It comes in a small pressure can, which holds just enough to do two valve covers. I reused the metal spacers which were in the original gasket, cleaned all mating surfaces with disc brake cleaner on a rag, applied a thicker bead than the instructions called for, and carefully applied the spec'd torque in a cross pattern.
The 4-cyl valve covers are known for being "wet", and this job hasn't wept yet. One note...if you use this stuff, do it right the first time, it's the devil to break it loose once it's on.
From: David Breeze
You can re-use the current bent steel cover if use use a hammer and a block of wood to restraighten it. However you do need to buy some aftermarket items (not sure what they are called) which are available at many auto parts stores. They are simply pieces of thick stamped steel which you put between the bolt head and the rocker cover which allow you to torque the bolts tighter. They spread the tightening force of the bolt over a larger area so that the bolt heads will not try to pull through the cover and bend it. This in conjunction with a little RTV silicone between the gasket and the cover fixed mine several months ago.
From: Daniel S. Spencer
According to the Haynes manual, it is possible to remove the rocker arm covers without removing the plenum/intake manifold. I tried to get the rear (trunk side) off this way, and could not get it with the tools I had available. (I think that with some small sockets and extensions of exactly the right size you might be able to do it). Here's how I did it:
From: Sketch