Expansion Tank Floater

[Purplecty]

When I purchased my Imola 4.6, the expansion tank had a hairline crack in it. I replaced it with a used (had slready been replaced but notnsure when as it had old BMW stickers on it) Genuine BMW Made in Italy tank from a friends Imola 4.6 parts car. I noticed the stick on the float is partially missing (seems to be very common) and I am unable to tell what the correct full level is when cold. The past couple days, I have been getting a check coolant error on the cluster but upon restart it never comes back. I check it in the AM on a cold engine and I can always visibly see coolant in the reservoir when opening the cap. I feel this may just be a level sensor issue or just the float getting stuck somewhere causing the error to pop up? There are no leaks at all under and where I park the ground is completely dry...