Done:
https://www.imcdb.org/vehicles.php?make=Rex for the Chinese recent models
https://www.imcdb.org/vehicles.php?make=AB-Rex for the Swedish mopeds
https://www.imcdb.org/vehicles.php?make=Rex-Motoren-Werke for the old German mopeds
https://www.imcdb.org/vehicles.php?make=Rexworks for the American heavy equipment

There were just three Romanian tractors in addition to the two Swiss bikes, I think these tractors should be listed under UTB like all the others.
I keep the links here for reference
https://www.imcdb.org/vehicle_1150100-Universal-533.html
https://www.imcdb.org/vehicle_1153430-Universal-445-V.html
https://www.imcdb.org/vehicle_937599-Universal-445-D.html

I'll do the split for the Rex vehicles later

https://www.imcdb.org/vehicles_make-Universal.html
Swiss bikes: https://www.imcdb.org/vehicle_312217-Universal-600.html
https://www.imcdb.org/vehicle_1629529-Universal-B50.html

https://www.imcdb.org/vehicles_make-Rex.html
German mopeds: https://www.imcdb.org/vehicle_260816-Rex-17-1955.html
https://www.imcdb.org/vehicle_650214-Rex-Monaco.html
https://www.imcdb.org/vehicle_290399-Rex-Piccolo.html
https://www.imcdb.org/vehicle_83568-Rex.html
https://www.imcdb.org/vehicle_1394442-Rex.html
Sweden mopeds: https://www.imcdb.org/vehicle_1393092-Rex-Midget-Sport-1938.html
https://www.imcdb.org/vehicle_196401-Rex-Rexoped-1955.html
https://www.imcdb.org/vehicle_362291-Rex-Z%C3%BCndapped-1954.html
USA construction vehicles: https://www.imcdb.org/vehicles_make-Rex_model-Pactor.html
https://www.imcdb.org/vehicles_make-Rex_model-RexRoll.html
https://www.imcdb.org/vehicle_21517-Rex-SP-700-1979.html
https://www.imcdb.org/vehicle_27967-Rex-SP-910B.html
https://www.imcdb.org/vehicle_17187-Rex-Trashmaster-3-70A.html

I finally found what caused that issue
It should now be fixed (tested in Firefox/Chrome/Edge, crossing fingers for Safari...)

I thought it was the fault of the ads, but no, it was just my CSS code
I wonder why I could not reproduce the issue back then: I fixed something related to that a while ago, but it solved only a part of the problem, as yesterday I noticed a case where I had the issue myself.

I added new makes for these.
For the Hydrodyne ones, it seems that name is part of the make, so I listed it as such: https://imcdb.org/vehicles_make-Star-Hydrodyne.html

This is yet another Star company ? https://imcdb.org/vehicle_1165366-Star-Mazda.html
And https://imcdb.org/vehicles_make-Star-Car_model-Hydrodyne.html not sure is Make Star or Star-Hydrodyne

Thanks, fixed. Sometimes it becomes confusing with all these links between pages. I also recently updated the links between all the ancestors and makes related to Daewoo, that was quite complicated

Star Car link in there is wrong, https://imcdb.org/vehicles.php?make=Star, should be https://imcdb.org/vehicles.php?make=Star-Car

If they are related and the Bristol brand is a name shared between companies, they should stay together. Like Renault or Volvo, where cars and trucks are made by different companies, but using the same "brand".
But that seems a more complicated case indeed And Bristol being a city, it does not make clear if they really "share" a brand or both use the name of the city. Since they are not complete strangers, I think it is easier to keep both under the same make on the site.
Another edge case was this one: https://www.imcdb.org/vehicles_make-Fiberfab.html
The German company was founded by someone from the original US company, and since they shared some models under licence it is easier to have both listed as only make.

I'm wondering if Bristol should be split between cars and commercial vehicles:
https://en.wikipedia.org/wiki/Bristol_Cars
https://en.wikipedia.org/wiki/Bristol_Commercial_Vehicles

In fairness, the Tramway company and the Aerospace company were founded by the same person so possibly not as straightforward as I first thought.