I had a similar problem with one of the retainers for the lower fulcrum pin. One of the bolts snapped and the car lowered quite a bit on the offending side.. I was very fortunate that I was only about a mile from home. I limped home and replaced all of the lower fulcrum retaining bolts... The broken of bolt was easily removed from the front x-member.
Original fulcrum bolts are grade 5 fasteners. I had stupidly assumed that a grade 8 fastener would be superior... not so much. The grade 8 fastener will snap faster as it is a harder fastener. The factory (Rootes) used grade 5 for a reason... You can identify fasteners with several methods... plating is one. Zinc fasteners are grade 2 or 3, Black phosphate fasteners are black oxide (grade 5) , and grade 8 fasteners are Gold (yellow) Cad. In all of the years I have been restoring Brit cars, the only grade 8 bolts were for the caliper to the stub axle. You should NEVER use chrome plated ( or stainless steel) bolts for anything in either the suspension or braking systems of any car that you'd want to drive on the street.
If Rootes thought a grade 8 fastener would have been a safer option, believe me, they would have used them... The last thing a manufacturer wants to do it take risks,