Men's Shed problem: how to refit new timber slats to concrete garden benches when the concrete bases are too full of aggregate to allow new holes to be drilled.
Solution: remove the head of the old bolts (a single one near each end of the slat) and weld a steel plate to it. Then drill 4 new hole in said plate and grind the weld down enough that a new slat will fit. Bolt new slats into place after repainting the concrete bases. Works, looks good as well.