Can an old rosette “iron” that's starting to stick be reconditioned?
I am going to assume that your chrusciki is cast iron.  I have been collecting and using vintage cast iron for 30 plus years and use the following method for reconditioning pieces which have lost their seasoned finish. Your irons must be able to separate from their handles, unless the entire piece is cast iron.


Separate all non-cast iron pieces from the cast iron pieces.
If there are crusty bits stuck to the cast iron remove these.  I use a variety of methods including fire, scraping, and soaking in a hot water bath for 15 minutes or so.  Soapy water is only okay before skillet is seasoned, never after.    Keep the cast iron off porous surfaces during the soak as rust may form and be difficult to remove from them 
Dry cast iron pieces and apply heavy coat of fresh cooking oil to entire piece.
Bake  on a foil covered cookie sheet in a hot oven (350-375) for up to 1 hour.
Let cool, pieces may be sticky and this is normal.
Store on wax paper until first use.
Use as recipe suggests.  Clean up irons using hot water only and a cloth of          some type.   
To keep seasoned, dry after cleaning, wipe with a paper towel dipped into fresh cooking oil,  store away from moisture. Pieces don't need to be dripping with oil, just lightly covered completely.  Can repeat steps 3-6 once yearly.