statute of limitations on repairs/sec dep?

California.
Portion of security deposit was retained due to "damage" to hardwood floor. There is no visual damage to the floor. LL upon move-out checklist admitted the floor looked great and since the floor had just been rescreened a year ago, did not need immediate rescreening prior to next tenant moving in. Later, LL claims there is a "residue" on the floor which prohibits them from rescreening the floor in the future, thus retained a portion of the sec dep for a full sanding/refinishing. I was given a copy of various estimates and was told that the company with the most expensive estimate was the one they would use to refinish the floor. This refinishing was not done after I moved out which was 4 months ago.

1) If the LL has never performed such repairs, can they still keep that portion of my sec. deposit?
2) Is there a time limit when the repairs must be complete and are they required by law to send me the final receipt?
3) Do I have any say in which company they use for refinishing?
4) Side questions--can sec dep be retained for professional cleaning the EXTERIOR of skylight windows on the 2nd floor? Also for professional carpet shampooing when I already shampooed the carpet myself?