New landlord: dealing with damage: Cracked porcelain sink

[Lyle Cooper]

A tenant recently moved into my NYC rental unit. He needed the pipes under the bathroom sink tightened up. So I went by yesterday and let myself in. Fixed the pipes and as I was cleaning up I noticed a crack in one of the sinks.  (bathroom double vanity).  I look underneath and sure enough it's cracked and water is running out.  

The tenant moved in 30 days ago.  After the prior tenant moved out, I went to fix a few thing and cleaned the apartment myself.  Which included wiping down the sinks.  I didn't notice this issue.  I'm pretty sure it wasn't cracked when I went to clean it, but I cannot say that with 100% confidence.

How should I approach the tenant?  I don't want to accuse him of breaking my sink.  But at the same time, I don't want to eat the cost myself.  New sink, replacement job.  etc. 

I think the first email should be a friendly one saying something like "I fixed the pipes and as I was cleaning up I noticed a crack in the sink."