It broke a lot more than just this mod, so it's probably best to just wait and see if S397 manages to cobble together a fix first. We're going to lose a lot of unmaintained content otherwise.
The problem stems from mods transferred from rF1(or at least files that followed the rF1 format). S397 recently made changes to the engine file, I'm assuming to accommodate the Hybrid battery options. This has caused some sort of mismatch with older mod engine files. The goodnews...short term.... is that @redapg's online tools seem to correct the problem. Run the engine file through his online engine convertor and that should take care of the issue. You can also edit by hand to remove all the comment lines at the top of the file. S397 devs have at least noticed the problem and are, I'm assuming, investigating.
Could I ask how you got at the engine files? When I attempt to extract them using the MAS file utility from their '-MAIN.mas' for the vehicles I get the 'unknown mas key' message
I believe the older version of the mod had the files decrypted. I do not believe there was any physics changes in the later versions. I also think S397 fixed the issues with those engine files in the last update.