bathtub damage, use security deposit?

[Shelley A.]

The old tenants used used hair dye that stained the tub, when they left they were able to scrub off the dye but now there is a section of the tub- where about 18" x 8" of the tub enamel has been scrubbed off and is discolored and rough. Also there is a 3" diameter chunk missing from the top of the tub where something fell down on it. They tried to repair the 3" area by putting some material there to cover it up but it looks terrible. The tub repair people are encouraging me to refinish the whole tub because they say it won't match if I just do the bottom and it will only be a little less expensive. It will cost about $4-500. The tenants deposit would cover the cost of refinishing. I feel like my choice is to leave it and do nothing or refinish the whole thing even though only about 10% of the tub is damaged.  What would you do?