I don't like the Wick oil for use on instrument valves, but it's a great (if expensive) oil for use on tools.
Let me guess that when you first got your instrument, one thing you did NOT do was to clean it thoroughly -- i.e., flush it thoroughly with a water/detergent solution (all pistons, valves, and tubing). Did you perhaps ASSUME that since it was NEW it was also CLEAN? Not completely unreasonable, but often false.
One of the last things that's done in making a valved instrument is to lap the valves. This involves using "lapping compound" (basically a dust-like abrasive substance) to make the pistons function as smoothly as possible in the casings. If the instrument is then not cleaned, but simply shipped. Or if the cleaning is less than completely thorough, that lapping compound is still there and will mix with the oil you apply to make the valves function well. You'll end up with some degree of lapping compound sludge, and you can keep wiping it off the pistons and out of the cylinders, but until you THOROUGHLY clean the instrument, it will continue to haunt you for a very long time (while also lapping the valves more than you really want them to be lapped).
So that's ONE possibility.
The other possibility is that the Wick oil really does suck. I found it MUCH too heavy/draggy to use in EITHER my Mack Brass euphonium or my Wessex Tuba (which it came with). It got relegated to the garage/shop (for use on tools), and I use Yamaha Light Synthetic oil. The valve clearances on those horns are VERY close.
Those are the only suggestions I have at the moment. But in any event, you probably should CLEAN it thoroughly, and then ditch the Wick oil.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)