My Honda Shuttle intermittently leaked coolant. Trident Honda franchise replaced by radiator £398 but not the radiator cap (thanks!) and it still leaked, over-heated and blew the air intake gasket. I resolved the coolant leak problem myself by buying a new radiator cap by part number from America (£12 inclusive from Acura America or £30 and to be ordered from Japan/pay first/wait 3 months at your friendly UK Honda dealer).
An air intake gasket leak exhibits intermittent difficulty starting & white smoke but no coolant in the oil. Take the radiator cap off and the white smoke might disappear. Any garage will diagnosis either don't know or new head gasket £2000. I resolved this with a £7 bottle of K-seal. I have used this before and it did not work, here's why:
1. run the engine to be HOT, well hot all round, take it for a run or wait 20 minutes.
2. shake the k-seal whilst keeping your engine hot. shake it again for 4 minutes (if there is any residue left after application, you failed to shake it enough)
3. switch engine off if you must (if you don't understand the dangers here then stop and give up), introduce into via the radiator cap, the expansion tank approach is unlikely to work because of the heat/cooling issues.
4.be sure that your coolant path is clear: have a new radiator :-() or flush the thing out properly so that k-seal can reach the gasket.
5. after application run the engine for another 10 minutes to get hot k-seal flowing otherwise it just coagulates anywhere.
6. job done, test the car and believe it. You should have an immediate improvement that improves over 1-2 hours then again after 1-2 days. Some lapses can be expected in the gasket are often sealed again. TOP JOB.