Be careful not to use alcohol or oils to clean without first consulting with a trusted maker or repairperson. Treat your instrument the way you would a child. Do not leave it unattended in a hot or cold car. Look closely under good natural light at the suspected area. Try inserting a business card into the suspected area.
Many people miss open seams which can then spread.
A proper repair to a large crack involves removing the top and gluing the top crack flush and then patching with very small spruce studs. In most cases, if the repair is done carefully, the tone will not be affected. A good bow will make an instrument sound very different from an 'okay' bow. The choice is yours. A good indication of the need for re-hair is when the hair at its loosest hangs well below the stick, or if the hair feels greasy.