This is one of my favourites! Instead of blowing a reactor you got to protect 3 of them from getting destroyed by robots. Just grab the fullmap that's right outside your starting room and explore the shafts. There are tons of goodies like Gunboys and such which help you vastly to protect the reactors. On your first try simply memorize the level and decide which 3 to protect so you don't waste time on the other 2.

The coolest goodies are the Guidebot powerups (not all of which are avaiable in level 5):

Accelerator
Makes him incredible fast, you should use it together with Go Wingnut.

Fire Extinguisher
Quite useful whilst fighting those nasty Napalm Bots, he automatically uses it as soon as you started burning. OTOH quite useless since it's obviously built in! Let yourself get on fire in the combustion chamber of level 1 and see the GB help you even if there was chance to pick one up.

Guardian (30 secs.)
Make the Guidebot temporarily cycle your ship and fire on any robots encountered.

Manual Pilot
Mercenary addon only!

Reverse Anti-Virus (30 secs.)
Use this one in between a bunch of robots. The Guidebot sends out some beams which tame the bots for a certain period of time in which they even assist you in attacking unaffected bots!

Wingnut (30 secs.)
Let the bot use it and he keeps firing level 6 lasers on your enemies, it rocks!