| 1/ I'm sure you could buy the plastic face of the rev counter but splitting the casing is a tricky job to do yourself without making a right pigs ear of it. For someone else to do it for you might cost more than getting a second hand rev counter - try ebay for a complete rev counter
2/ Could be the seal which is located just below the cap. Unbolt the cap, check the seal and replace if required. Next check the connection from the bottom of the reservior to the tube. Then check the plastic reservior itse;f for damage.
3/ There are a few very good plastic panel repairers around. Most will completely eliminate a split, crack or even a hole. Just this board for repairers by doing a search. | 
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