Hello Hope
I have rambling rector too. Mine looks very healthy after having a very hard pruning last year. It' s loaded with buds but it's about three weeks late in flowering. Have you tried a fungal spray?
Marjorie

Could it be black spot (if the spots are a very dark brown?) If so spray it with Rose Clear.

Generally at this time of year the brown spotting (which rapidly spreads once the first spots appear) is downy mildew. It's a beggar to get rid off. I spoke to the resident expert at David Austin Roses last year, and they were spraying twice weekly to keep their stock clear! It's worse when the weather's a bit damp. I've had to prune all my roses down hard and start them off again with a spraying regime recommended. (I don't use sprays at the garden centre, so I'm concentrating on keeping the stock healthy, well watered (from the bottom, and not by overhead watering) and have made the decision not to stock roses any more because of my close proximity to cress beds and damp conditions. Remove the spotted leaves and spray regularly to keep on top of it