Welcome to ATP, DarrenP!
Yep, definitely not the damage of any of the bean beetles. And with your mention of "slime" combined with the photo I agree, slugs for sure.
If you want to save some money you can have great fun going out with a flash light at night and "harvest" the slugs. Just pick 'em off and dump them in a can for disposal somewhere else. (My preference was to toss them to my ducks! 'Tis a great site, and sound, to see them do their best to slurp down those slugs.."mack mack mack mack slurp!"
If your garden isn't too large you could also go lay down some boards or something else in the rows. The slugs will take cover there before daylight arrives to sleep for a while after enjoying your bean foliage. Just lift up the boards and snatch them up and do what you like with them.
Wishing you a good garden and an even better bean harvest, especially since you mentioned those beans were inherited from your mother's garden.
Shoe
