If you don't know when the belt was last changed, change it!
As far as I understand, the belt problem was never one that affected all engines.
My engine (age unknown) hasn't got the blob of yellow, but HAS had a modified pulley fitted
to prevent the belt sliding off the pulley and shredding itself.
When you take the front cover off, if you find a large build up of rubber 'dust', you can be sure that your engine suffers the problem and will need some modified parts.