Confusion ignorance High pressure tyre valves

I need my first set of replacement tyres for my 5 year old Broadway. I have metal valves on alloy wheels. I have looked online at all the usual tyre dealers/fitters. I then contacted several to make sure of two things

1 They could actually fit my vehicle in (size wise)
2 They would fit/replace the high pressure tyre valves

I have been met with a wall of ignorance and confusion. One fitter told me I didn't need them, several remained silent for several seconds before asking if I had rubber or metal ones and they didn't have them in stock anyway. Others stated they simply replace the inner valve not the stem as it is metal. Others stated they had to order them in specially and I would have to pay for them as they were not 'standard' valves. 
With the number of motorhomes on the road I would have thought they would have changed a few tyres by now and know what they were doing. 
What I would like to know is can I simply have the inserts changed, do I need totally new valves, has anyone else successfully had new tyres fitted?
Where did you go?

With normal steel wheels it is well worth having the metal valves fitted, but I think you are wise to query what can be fitted to alloy wheels to avoid problems with different metals that can be an issue in the case with aluminium.
Sorry cant be of any help.

Why change the valves, on the Autotrail I had with metal valves I never changed them in 12 years of ownership ,rubber valve I can understand changing as uv deteriorating the rubber

The valve insert was changed as this was removed to deflate the tyre and a new one inserted to inflate

I always replaced the metal valves which I supplied, only a couple of pounds each,, but asked the fitter for approval before fitting. They were on steel wheels

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Do you make that many miles, that you have to replace the tyres after 5 years.
In Europe up to 10 years of use , and then preventive replacement, is normal, if you make little miles.

If you have external sensors for TMPS,  the TR600 series is most likely OK , because they are made for 95 psi cold pressure, and wont bend under centrifugal forces at higher speed, so wont leak then at the hole in the rimm.
Metal valves certainly no bending.
The TR600 is snapp in valve with about same price as normal rubber TR4?? Series, so can be renewed every tyrechange.
Metal valves, only the rubber rings have to be renewed, but is seldom done, so in practice can be unsaver then the TR600.
And if you dont have sensors, bending wont happen.

My Nuevo is 2008 Reg and I have just had a metal valve changed as its seal was leaking against the alloy rim.
I didn't change tyres at 5 years, was advised to, and did, check the tread, walls etc annually with no problems.
I think I made an executive decision to change applicable tyres at 10 years tyre age although they seemed to be OK.
Normal wear, especially on fronts, may overtake this process.

I had to have a tyre replaced on my Devon (Mercedes)by Kwik-Fit. I had to go back repeatedly due to the tyre going down slowly. After many conversations they finally agreed to fit high pressure valves. To my surprise they replaced them on all four wheels. Even a large company like Kwik-Fit are not knowledgeable on high pressure valves. Also if you buy them on line beware there are different lengths. I have alloy wheels and they got the wrong size and had to reorder.

For information, I've copied the valve specifications form the Continental Data Book below:

*)43 GS 11.5 are snap-in valves approved for up to 4.5 bar.
38 G 11.5 is a valve for the hose.
Standard rubber valves are only approved for up to 4.5 bar in service.
TR 600 XHP and TR 602 HP (ETRTO V3.23.1+2) are reinforced snap-in valves approved for up to 5.5 bar. 40 MS (ETRTO V2.04.1, V2.05.1) are metal valves approved for pressures up to 6 bar and higher.

The CP tyres recommend TR600 XHP, TR602HP or 40 MS valves.