Amen to the repair kit Bill!  It's amazing what can go wrong with a stove out on a trip, even when you've broken it down and completely cleaned and operated before a trip.

I like the oil tip - probably some stuff in first aid kit that would do it as well - but I also carry a repair kit for my Dragonfly which fits in the bag.

Cooking oil will usually restore the gasket well enough to get you through a trip.

I've gotten pretty adept at field maintainence of stoves over the years.  I also bring spare o-rings and parts.

Ploder,

A few years ago I was soloing up on Quetico lake. I tested my gear before I left, but my first night up there my stove wouldn't work (the gasket on the pump and the valve had failed so no pressure would build and any pressure that DID build simply pushed fuel out through the control valve). I was fine cooking on a fire for the during of my trip but that got changed when I had three days of soaking rain. I couldn't get anything to catch fire it was so wet. I had to turn back because of it.

About 10 years ago my group entered through Nym in August and used and outfitter (name withheld) for canoes and a couple other things, including a burner.  The night before we looked it over and threw it in the pack. The outfitter said they expected a fire ban soon because of the lack of rain.  Our first night we realized the burner was broken and not usable.  Luckily we were able to cook over a fire for the entire week cuz there was no rain for the first 5 days of the trip.  Found out on exit that there was a fire ban established day after we entered.  It was very dry, and we were careful by choosing our campsites based on risk with a dry forest and cooking over the fire. 
I learned a couple things that trip... 1) always bring 2 burners or at least test your burner before you enter the park (man we felt stupid), and 2) cooking over a fire during a fire ban can be a necessary risk.

Based on what I have read and discussed with rangers, I believe what snow dog said to be the case.

My take has always been that if you enter under a fire ban, you are under a fire ban until you receive word (from another party or a ranger) that it has been lifted.  I wouldn't let a fire ban stop me from building a fire that I believed to be a matter of life/death, of course, but short of that, it's a luxury.  I'm not risking a fine or worse (such as starting the park ablaze) for a luxury.

If you enter and there is no fire ban, then you are allowed to have fires until you receive word (from another party or a ranger) that a ban has been put into effect.  At that time, I think you are morally, if not legally, obligated to follow the ban. 

Hey, I love a campfire as much as anyone.  I will have one every night if I am not under a fireban.  But I'm not interested in setting the forest ablaze and footing the bill for putting it out.

A long time ago we went in from Beaverhouse when there was a fire ban.  You could use a gas stove but no fires.  It was great no bugs and the sun shined every day.  A week plus later we were paddling out on Quetico Lake and had stopped on a sand point.  As we were walking on the point, a plane landed and the ranger basically asked what the hell we were doing in the park as the park was closed.  We showed him our permit with our entry date so he didn't do anything, but he advised that we had to leave the park right away.  So if it gets dry enough, they will come and kick you out.
Westwood

Exercise your best judgement.  Remember the forest you save likely contains you.   

Judgement goes both ways.  I was once on a trip and after several days of no rain, bone dry ground, wilting greenery we self-imposed a fire ban.

I've had some downpours that seemed like a lot of rain, the rivers certainly gushed.  All of it ran off the surface.  Not even 1/4" on wet ground before I was kicking up dust.

Campfires are nice, but they're luxury.  Some places have ugly steel barrels dug in to the ground.  That's how you know the area is frequented by idiots who want more than they think.

I believe that common sense should be your guide.
One year I picked up my permit in Atikokan and they had a fire ban on even though it had been raining fairly heavy and the forecast was for more rain the next few days.

I asked the lady whether or not the ban would be lifted in the next few days?
She said that it wasn't their call but that obviously the fire danger was greatly diminished and I should use my best judgment.

I said that with the cooler temps forecast for start of trip that a nice warm campfire was something I looked would welcome after a long day on the water.

She smiled and said they wouldn't want anyone suffering hypothermia or being miserable when the conditions had obviously changed but the ban hadn't been officially lifted yet.

When I hit Beaverhouse, it was raining buckets and at the portage to Quetico lk, I ran into a Father and Daughter tandem who said the last few days had been miserable with the cold/wind and rain, but they were afraid to build a fire becasue when they went in a fire ban was on.

I told them it still was and what the ranger gal told me and that I planned a fire that night, ban or no ban.
The Father looked a little sheepish and the daughter said something like " I told you they wouldn't care, it's been raining cats/dogs for the last 3 days.

I can't imagine a back country ranger going without a fire when the conditions changed before the ban could be officially lifted, and doubt very much they would expect you to do the same.