2003 Toyota Corolla Timing belt tensioner oil leak and serp

I have a 2003 Toyota Corolla CE 4cyl car with 79k miles on it. I went to the Toyota dealer to get the inspection sticker and regular oil changed. The dealer told me that they noticed a minor engine oil leak in the "timing belt tensioner". He mentioned something about "o-ring". They also noticed that the serpentine belt was dry and cracking. They were asking for $180 and $118 for each respectively.

I tried to research this issue online but have not come across much information regarding "timing belt tensioner engine oil leaks". All I found was the tensioner itself failing for several people.

How can I make sure that there is actually an engine leak in the car. I don't notice any oil in the driveway. I tried to look at the engine but I don't see anything besides minor oily debris. I had asked the dealer if the engine oil they drained was significantly less than usual but they couldn't comment on the quantity of oil drained.

Also, how much work is involved in fixing this issue if it is actually an issue. I have done some repairs in the past so I would really appreciate it if I can get some tips on how to do the repair myself and what tool would be needed.

Thank you in advance