Habitation Door Lock

The habitation door lock on our Rienza has always been a bit vague and had no return spring but worked so I ignored it. Last trip it wouldn’t unlock but after a bit of fiddling locking and unlocking I managed to get in. It seemed to help with  a dose of WD40 in the lock in until yesterday. Again WD 40 helped.
From this I am wondering if a new barrel would solve this problem. I did find a post about this problem but can’t find it again so I apologise for a repeat post. I have found a full handle that matches at £50 +. It appears to be an Oberholz lock.

These from a quick G**gle for WD40 car lock:

"Can WD-40 damage locks?

This multi-faceted product has limitations – it should never be used to lubricate locks! The main reason for this is that WD40 is not a true lubricant; it is a water and oil displacing solvent. This means that it can actually remove any lube already in the lock, leaving it dry and susceptible to sticking"

and

"WD-40shouldn't be used in door locks or ignition locks. It dries out and turns to goo, which can cause the tumblers to stick. It was initially meant as a de-rusting spray and general-purpose lubricant (say, door hinges). Locksmithsrecommend using Teflon spray lubricant inlocks now."

Point taken Rodger. It was the only form of lubrication to hand at the time and it did improve matters. My question was more related to changing the barrel or outside handle. Once I am at home I will take the handle off for a proper look at what is going on. 
I seem to remember something about graphite being used for lock lubrication. I will look into this later.

If you have a sticky lock barrel rub a pencil over the key and try it in the lock, you can do it more than once, the graphite from the pencil will lubricate the tumblers .

It feels worn and not very positive when you lock and unlock it. Not being a locksmith but have some mechanical knowledge I am wondering if the plungers are sticking in. Maybe as you said Roy the graphite will help. 
Until we get home I can put the dead lock on rather than using the key. It’s probably more secure than the original door lock.

What you need is graphite powder in a puffer pack from graphite trading co.  It's amazing how good it is on all locks

Our hab. door lock felt sloppy and vague when locking/unlocking. Eventually it locked us out. I took the cover off the inside of the lock and cleaned and lubricated the mechanism (not the key barrel)  and it's been fine ever since. 
On a related note, you can buy lock lube sprays which are good, a generous squirt can clear a lot of muck out of the lock barrel - but WD40 is a complete no-no for locks.

I feel serious told about WD40. The idea of do anything spray certainly dosnt mean what it says on the tin. I found some stuff on Amazon that says it’s a lock spray so I will take the whole lock in the workshop and give it a good cleaning and re lubricate it all.

After waiting the my covid to clear and the lock oil arriving I have managed to sort the habitation door lock.
I removed the five screws that I could see on the inside and the outer handle and the lock bit from the inside came off. As I took it  off three small self tapping screws and a connecting barrel fell out ???.
Once on the bench and a bit of sussing and boggling I found  the screws were meant to hold the lock to the inside of the door and the barrel is to connect the outer lock to the inside parts. 
After cleaning everything and lubricating the inside parts I left the barrel with the lock oil in it to soak whilst I sorted the issue of the screws and the connector. 
The inside bits were fastened to the inner skin of the door with tiny self tapping screws so they were replaced with bigger screws. The connector has a threaded hole in it so I assume its meant to be locked on to the lock barrel with a screw. Strange as it might seem it is tapped 6BA so I found a grub screw to fit.
After cleaning the inside of door the lock is re fitted and works as it should so thats a satisfying result. I used Abus lock oil as recomended by a biker. Thinking being that bike locks are outdoors. 

Sorry I didn’t follow up the repairs the Covid seemed to fuddle my memory.
Once I put it all back together and oiled the barrel it seems to have sorted the problem. I think originally the fault was more things falling apart between the barrel and the inner lock. The key still dosnt spring back to the mid position but it locks and un locks so that’s a plus. 
The inner lock is a bit stiff now so I might have another look or wait until eases it’s self over time. I have oiled all the other locks with Abus oil to justify the cost and it seems to have eased the lock on the water filler cap that was stiff.