New AU3 Wagon front brake shudder only at 100kmh

[asimplelife]

Bought another wagon that seems to have been well looked after.
1st owner 13 years as a daily 150,000km. Looked after it probably until the last year or so then let things go a bit until trading it in.
2nd owner 7 years garaged 10,000km. Seems to have fixed all the issues he was aware of.
Car drives like new. No problems with the brakes at all up till 80kmh.
But when I take it on a longer trip, at 100kmh, then brake hardish from 100kmh, I get a shudder through the steering wheel.
This has been since I bought it a few months back, every time I do this sort of drive, and it hasn't improved.

After inspecting, the right front wheel feels much hotter than the left.
Took it to my mechanic. He says while nothing wrong, he believes the right front brake caliper could be sticking.
He thought it might come good after driving for a while, after not being driven much for 7 years. But it has not improved.

His suggestion is to replace the AU3 front right caliper from my previous AU2 wagon which I am currently stripping. I had no problems with the AU2 brakes during 2 years of driving it.

Before I spend that money, just wanting to check if there might be any other suggestions I could be trying first?