sometimes all you need to do is change things up a little to get that final improvement.
Example: former American record holder in the 10K Marcus Nenow ran 27:40 by running 10 miles 2x per day = 130 per week. Mostly just tempo type running/steady states.
added track work and dropped it to 27:20 (-20 seconds off)
So for you...whatever you are not doing - do that
If you are not doing track work - do that
If you are not doing long runs - do that
If you are not doing tempos - do that
If you are doing all of that then you may need to make a more significant change:
1) by doing more mileage or 2) by doing less (either will probably work)
If you go for the do less mileage route - which is what I would suggest - the goal is to run fresher, faster on less mileage with more recovery. At the height of my best running I cut back to just 25-40 miles per week over a 9 month period and dropped by Pr's from:
31:26 - to 29:53 for 10K
25:30 - to 23:45 for 8k
etc
I was only running four days per week (so that everyday but Sunday I was running fresh). This enabled me to run tempo/steady states on Tues/Thur at a pretty good clip. Raced on Sat and ran longer about 15 miles at 6:00 pace on Sunday.
If you decide to do more mileage - you basically want to cut back on the quality workouts and just hit mileage at an easy pace. Maybe go as high as 130-150 per week. Do this for 8-10 weeks and you will have a bigger engine and can then start doing faster stuff again. this should give you the engine to run 30 seconds faster.