By now we're all familiar with the use of the STC3064 cam kit and cutting off the extraneous bit of metal and we know these work well, BUT...
Getting the spring onto the plastic cam AND into it's correct locations can be a long process and hard on the fingertips and patience.
Here's the (well, an) answer- cable ties.
First the easy one. Use the first cable tie, with key in lock, to hold lock tab out of the way, like this:

Now for the spring. The problem is holding it under tension and connecting all the components at the same time, traditionally requiring 3 hands. The solution is to pre-tension the spring and use a cable tie to hold it under tension.
To do this (and I apologise that I don't have better photos, but again that would require 3 hands) put the spring onto a handy sized bar, screwdriver, whatever and prepare a small cable tie in a loop. put one end of loop under small arm of spring and press spring/ bar/ cable tie combo on table top.
Bring long arm of spring over into its tensioned position and tighten cable tie to hold that tension. Note you don't need as much tension as pictured.
Spring is now compressed and held compressed by cable tie.
Remove from bar and assemble handle/ cam components. They just drop into place easily without battling the spring.
Gently move handle to ensure everything assembled correctly, insert new roll pin, cut cable ties, spring releases.
Take other cable tie off lock arm
Test
Job done!
Pics of in progress solution:

Orangebean wrote:

By now we're all familiar with the use of the STC3064 cam kit

I'll be honest and admit I wasn't even aware such a kit existed. Both my front door handles don't fully return unless you push them back in, does the kit cure this? Never caused me a problem other than not looking right.

Not returning is the first sign of the wear. They then get stiffer as the wear increases. Ultimately the roll pin which acts as a spindle for the cam lever can fall out.
Funnily enough, as the drivers we don't tend to notice. It's usually when someone else drives the car they mention the stiff door handle.
EDIT- or, of course, when you suddenly can't pull the handle to open the door.

Or, when the wear is so bad, the handle comes off in your hand...

In theory that could happen. I didn't realise the handle part actually came out of frame until I had cam etc out and handle fell out. Poses another dilemma though. The stub on the aluminium handle that slides in the cam also starts to wear and become more conical. Even with all the repairs, which get it back close to showroom, you can never get it perfect unless you can find a spare handle with a, as designed, cylindrical stub.

Sloth wrote:

Or, when the wear is so bad, the handle comes off in your hand...

Oh it definitely does :) Ask me how I know...

LOL
So how do you know Sloth?!
I see this post now has a little start beside it in Oily Bits menu. Wonder what that means?

It's been stickied so it will always stay at the top.

Ooer, I feel a bit special now :)
In that case, if this is going to be used for reference, Google "the definitive fix for stiff P38a door handles", the topmost link will take you off to another site where the background is discussed in detail, how to get the handle off without breaking a key part, exactly which bit of metal to cut off the handle assembly etc.
Doesn't address the spring/ lock/ cable tie fix that I refer to in this thread though. I've got dibs on inventing that (or being the first to put it online).
When faced with any problem, if you can't solve it with Duct Tape, you will with a cable tie!

So from now on it will be Sir Orange then!

Has to be better than Mr Bean!

That should have been too obvious, there's more clumsyness needed to deserve that title.

I need to do this to all four of my doors as they are all stiff. Is there a preferred supplier for the cam kits? What kind of money are they?

STC3064 for drivers door. STC3063 for LH door.
I use LR Direct £3.32 inc vat, but all the usual suppliers will sell them.
Usually only the drivers door that wears enough to get stiff, so it's possible that the others are just a bit corroded and will respond to a good clean and lube.

ok, cheers. Hoping to have a look in the next day or so.

From memory, the rear doors don't have the cams in them that the front doors have - so probably a couple of good shots of a lubricating spray like WD40 will work better on the rear doors.

Worth a shot, cheers.

Thanks for this, I need this for both front doors.

I've just done my driver's side handle with this technique, and it works just great. I actually got a handle from a scrap one and rebuilt its lock because the little lock tag thing had broken on mine, but I reckon I can work out a way to do a repair piece for that. My driver's side door lock has actually jammed solid, but the pins in the breaker were so close to the originals that with a bit of swapping around and a very small amount of re-profiling two pins I now have a totally working lock - and a handle that isn't stiff!

Gordon, rebuilding the lock barrel is probably worthy of a topic/sticky all of it's own..