Recently I noticed a burning oil smell when parking our 2003 VDC 3.0L H6 after a drive, despite not seeing evidence on the floor of my garage of any serious leak. Brought the car into our very good independent garage and they found (and I also saw) an oil leak, which they said was coming from the Valve Cover Gasket and the Front Timing Cover Gasket.  While replacing the gaskets, we'll have easy access to the spark plugs and since the car is at 118,500 miles, just 1500 miles shy of the 120K inspection when sparks should be changed, might not be a bad time to change them. They won't charge extra to change the spark plugs with such easy access during the repair. Any recommendations for good quality spark plugs?

Ahh teh spark plug wars!!! Gotta love the hype...I don't know how or if I'm going to get blasted here but hey lets go for it my 2 pennies worth.

 

You have three choices and basically the only difference is conductive metal types and marketing.

 

The metals are Copper, Platinum and Iridium.  Copper is by far the best conductor of electricity out of the three, and coolest running.  Down side is it is also the most susceptible to corrosion and as a result they don't last as long.  Platinum, has the least conductivity but the best corrosion resistance but they do have a tendency to over heat which further decreases the transference of electricity.  Iridium in considered the middle of the road, its conductivity is better than platinum but less than copper, corrosion resistance is better than copper but less than platinum.  They will overheat faster than copper but not as fast as platinum.  They do generally last longer than copper which is why they are also about twice the price.

 

Copper plugs have to be changed around every 20K the other two can last 40K but the performance is not as good.

 

Hope that helps.

Subaru's, particularly newer generations, are not forgiving with ignition components, sticking to stock or getting Subaru/engine specific advice for any upgrades is ideal.

 

I would use the Subaru OEM platinum plugs-  they are amazing. I have two of the exact same engines/vehicles as yours in my fleet.

the ones i've changed even with high miles have always been in excellent condition.

 

and yes - removing the valve covers makes the job much easier - you are wise to do both at the same time.  unless there's a compelling reason not to, i generally do valve cover gasket and spark plugs at the same time on those H6 engines.