Catalyzes the 2'-O-methylation at nucleotide C2498 in 23S rRNA. cytidine(2498) in 23S rRNA + S-adenosyl-L-methionine = 2'-O-methylcytidine(2498) in 23S rRNA + H(+) + S-adenosyl-L-homocysteine Monomer. Belongs to the class I-like SAM-binding methyltransferase superfamily. RNA methyltransferase RlmE family. RlmM subfamily.