usually they change the timing belt every 100K kilometers or even less if you consider the traffic when your engine is running but is not registering in your odometer. you probably need to change yours.

if you change the timing belt, you replace the tensioner bearing.

pwede mo din isabay yung camshaft oil seal since same side siya ng timing belt ng corolla. not sure about the pulley oil seal although same side din siya.

when you remove the timing belt cover kasi accessible the itong mga ito. make sure to buy the original oil seals para sure the walang leak. mahirap kung ibabalik mo pa.