Any wing spars on ageing aircraft have cracks. Most of them are very small and only detectably by special inspection technologies (i.e. eddie current inspection), some of them are lage and visible during routine inspection.
There are crack findings in service for any type of plane of any age, this normally leads to SB´s (Servive Bulletin) by the manufacturer where all operators are told to do some sort of inspection, replace some fasteners by oversized type, do coldworking of rivet holes, install some sort of doublers or reeinforcement brackets or something like this. The authorities are notified, and if they think this is a larger problem, the SB is made mandatory by releasing an AD (Airworthiness Directive). There are hundreds of AD´s every year regarding cracks for different types of aircraft. This is all totally normal and just a consequence of the fact, that large transports are not designed to last forever, but to make profit with the least ammount of maintenance. So they are designed to take some cracks, even in the wing spars, without consequence.
For the Airbus B4 models there had been lots of crack findings and structural rework or reinforcement in the past (but even less than on other aircraft types by other manufacturers) but the only recent problem I know at the moment, regards gear rib 5 (the wing rib where the main gear is attached to). This seems to be nothing to worry about, this rib can be inspected visualy without problems and can be replaced in complete if neccesary, or just repaired locally if the cracks are small enough. If no cracks are present, reworking some fastener holes and installing oversized fasteners will increase service life of the parts and avoid further cracking.
Enjoy flying the B4 as long as they are existing, no need to worry