forks shouldent need lube, if you want to clean the upper legs tri flow is the only thing i would use. but wipe off any access. forks have an internal lubing system to keep themselves oiled. the dust seal works like a windscreen wiper over the fork legs so most of what you put on will be wiped off. tri flow is very thin and will keep the dust seals soft enough to do there job.
a service one a year is good for them, seals will be replaced and the oil will be changed. when we service forks we oftern find dirt in the lowers. dirt causes scratching, and scratches cause leaks.