Went through the Crosman crappy stuff phase-that doesn't count.
First real airsoft implement was Tokyo Marui MP5K PDW which I still own. Love it, love it. Bought it in 2005, took it apart for first time this winter-looks excellent inside. Replaced bushings with Modify bearings and replaced spring to get it back up to stock 280fps. Had to reshim because I installed the bearings, but the old shim job on the bushings was perfect. I still have the plastic bushings - they did not need replacing, I just did it because I had it apart. I cleaned it up and put every other part back in for another 50,000. Oh yeah, forgot, I put a Modify metal spring guide in and replaced the o-ring on the piston head, again it didn't need it as can be seen in the picture. I could have put all the stock parts back in. After 50-70 thousand cycles I would call this an excellent gearbox:
Nice and light and compact and useful in an airsoft operation: