They both do,
http://www.mitsubishielectric.com.au/
https://mhiaa.com.au/index.php/products/wall-splits
We've had a better run from Mitsubishi Heavy Industry units.
The "spring retainer" is just a spindle extension, http://www.bunnings.com.au/kinetic-20-25mm-spindle-top-extender-4-pack_p5050144
The grubscrews will have to be loosened to get them off then the spring should just come off the original spindle.
A soak with WD40 type stuff will help.
I think they are simply wanting you to do a service for less than they paid previously.
Sorta letting you they know what it costs or they expect to pay.
(I am fully aware that all services are not the same,i.e additional work at times depending on Ks etc)
Is it, or is it actually that the insurers are running the country?
I.e, forcing regulations/standards/checks etc to protect/reduce risk (and payouts) to their own industry.
So if the detector is passed and approved by a professional tester employed by the landlord, and it fails the next day and someone is burnt/injured, who is liable?