I have had good success freeing up stiff focus helicoids with Niftech Micro Bearing Oil. It comes with a very fine needle applicator and you can get it onto the helicoid without taking the lens apart in many cases.

'MICRO' Bearing Oil
1000 Series (Lubricants)
Product Number: #1030
Keywords: Bearing Oil Lubricants
''MICRO'' Bearing Oil renews old ball bearings.