Miata woes (p0421 & valve cover gasket)

[Curt Thompson]

So I've been having these problems for quite a while now - once in a while I get one solved for a few weeks and it comes back...
It's a 1999 Miata (base, California exhaust) with a bit over 170k miles

1. Leaky Valve Cover Gasket - aftermarket, OEM, torque to low end of spec, middle of spec, high end of spec, doesn't matter, always seems to leak.

2. P0421 (Catalyst Warm-up Below Efficiency). I had a new pre-cat installed just under 2 years ago, a year or so later I did new spark plugs, wires & coil pack - pretty sure i've changed plugs once again since then. CEL was off until 4 or 5 months ago until it started coming on randomly, now always comes on. I did a Seafoam treatment, MAF cleaning and replaced both O2 sensors and PCV Valve a few weeks back now, CEL always comes back on after a few cycles.

3, weak handbrake - it works ok after adjustment for a day or two, then gets weak enough that the car will slide slowly down any decent incline. The shop I visit when I'm stumped says it's not the cables - curious if anybody here thinks otherwise.

I'm thinking about trying to do the 2001 exhaust header swap ... any advice on that? Will any exhaust shop be willing to weld the bung in behind the 'rear' cat or will they be worried about doing something illegal (tampering with exhaust).

Not sure if there's much I can do about the valve cover gasket, (warped valve cover?) but open to advice.

I also need a power window switch if anybody's got a wrecked Miata laying around.

[Max Hayter]

May I suggest contacting Steve Lepper at Gearhead's garage - he is the guru of the Miata.

[Curt Thompson]

May I suggest contacting Steve Lepper at Gearhead's garage - he is the guru of the Miata.

Thanks for responding. Sure, I'll give that a go. I have started considering bringing it to the dealer and shelling out the 'big bucks' to at least get some good diagnostic results but I'll see what Steve has to say first.