I have a Marzocchi MZ1 fork. It uses an elastomer/coil for damping and a sealed hydraulic piston assembly for the lockout. The fork is very plush so I use the lockout generously when I am riding in the street. When I am engage the lockout during riding the fork is preloaded with my weight, so if I get off the bike and disengage the lockout the fork pops back up about 20mm. I've been leaving the lockout engaged when I am not using the bike, with the fork in the preloaded state. Is this a bad thing to do? Does it wear down the spring/elastomer if I leave the fork idle for a few days with 20mm of compression locked in?

So....nobody knows?

Leaving a spring/elastomer under tension all the time, can fatigue it and cause it to lose tensile strength. I assume? I dunno I wouldn't /dont, do it with my bike, or automatic knives, or gun bolts. Any spring I own, I try to store in a relaxed state.
JMO

Although......the spring in my deraileurs get left wherever they are when i'm done riding!

I take the springs out of my fork and lay them on my pillow at night. I also let the air out of my tires so I don't fatigue the threads.

Well Done sir!

My experience doesn't directly relate to your situation, but it's close. I have an older Cannondale Jeckyl with a headshock; at the time these front suspensions did not have a lockout feature. The only way I could stiffen up the fork for climbing was to compress the shock down as far as I could, which I often did. The result several years later is the elastomer is shot and the shock has no damping left- it's become a pogo stick. I'm only 105 lbs. and it's unlikely I would have killed the elastomer so completely at my weight. Took the bike to my LBS and was told that Cannondale doesn't make parts for that shock anymore, it would have to be returned to Cannondale to be upgraded to the current model for $350. I think I'll get by with the bike for another year and save up for a new MTB.

The lesson seems to be to lock out your fork while it's unloaded.

logically prolly not the best plan to leave it compressed but also prolly not a very big deal, especially since you are only leaving it compressed to teh sag height, if you where to somehow lock it out like bottomed out that would prolly be bad but i dont' actually know for sure

^rnorris, if you don't want the pogo-shock you could get a converter headset to standard 1 1/8 instead of teh 1.5 the headshock uses and then run any fork you get off ebay or w/e that won't save you money if you wanna get somthin nice, but if you don't car about weight you could get a used marz dj cheep and at least have a working

Sirti,
That's a good option and one that my LBS didn't offer- maybe they didn't want to deal with the conversion. I like the Jeckyl but hate this planned obsolescence that Cannondale seems to have built into the Headshocks, and retrofitting a more standard fork would be a way to avoid this. The bike is ridable, but climbing rough terrain isn't fun with a mushy fork.

my friends headshock cartrige blew and the ride was terrible so i know how you feel (although his bike is newer so we got a new cartrige for the fix), maybe ur shop didn't know about the conversion headsets, non-c'dale dealers sometimes don't i actually work for a c'dale dealer and one time a guy came in looking to go to a normal fork, apparently performance had never heard of a converter headset, so he was really happy when we could do it, i'd check with other shops around. I believe the headsets are in the QBP book (but i don't have one at home so i'm not posative lol) so really any shop should be able to order a converter headset, although idk if they need diff headset press attachments or w/e but a c'dale dealer should be able to help you out