Yeah, fork springs and shocks wear out from supporting the weight of the bike full-time and repeated expansion and contraction, fork oil from heat and churning, and fork seals dry out and get micro-leaks if not full breakage. A fork rebuild or shock replacement will help a lot.
I can't find any fork springs or monotubes with #680078 on the PS web site (
https://www.progressivesuspension.com/products/harley. Could that be the vendor's PN?
Note: It's been 10 years since I rode on the PS front *monotubes*, so they might have made changes since then, both good and bad.
Installed the PS monotubes (lowered version, PN 31-2501) on my '08 SEUC. Put about 26,000 miles on them in 2 years. New, really loved the smoothness (less road vibration), quiet ride, more stability (especially in curves), less brake dive.
By 20k miles, they felt pretty well worn out. Even with half-price labor att (winter special at dealer), the combined cost of parts + labor was high for only 20k miles effective use.
PS says the monotubes have "Lifetime Limited Warranty," but the warranty provisions specifically say it does
not cover 'normal wear and tear.' Of course, you also have to pay the R & R cost and shipping.
Good luck and enjoy the renewed ride.