Elbow Grease... It is a humorous reflection of the fact that some tasks can only be achieved by hard effort and human energy. Other countries have expressions that are near-enough identical. In French we have 'huile de bras' or 'l'huile de coude', which translate as 'elbow-grease' and in Danish we find 'knofedt', which translates as 'knuckle fat'. "More grease to your elbow" is indeed a correct english sentence, more specifically an idiom. Coincidentally, the correct, or more common form, of this particular idiom is "more power to your elbow", which also shortens to "Power to you!". This is a way of praising someone's success. However, it mainly stems from the sentence describing when something needs "more elbow grease", or someone tells another to "put more elbow grease into it", meaning that a little harder work or effort is required - that someone could put more effort into a task.
As a tribute to introducing me to Geocaching this one is in honor of the Camp Skylanders. You asked for it, it's out there now. You're gonna need a little "elbow grease" to find it!