Z1 tail light-bulb lifespan

Try owning an old HD Shovelhead. I always carried "2 - 1157" bulbs when I went out years ago, stripped down FLH with straight pipes for 25 years. When I beat up on the old FLH Bar Hoppin' &  hole shots and yankin' 2nd gear! Around town! Those were the days!
Not so know! I don't think I went over 40-50 MPH in the past 5 years on this Old Lady    Plus the new LED's are great! Plus they make brighter, more wattage for safety.

What bulb exactly have you been having problems with?  There is an 1157 configured bulb that has a vibration resistant filament that has solved this problem for me in the past.  I am not sure of the i.d. number...try 1034 or 2057?

Honestly I'm not sure, I'd just always swing by the auto parts store on the way home and replace it like-for-like

This article has good information. I just brushed through it. 

www.webbikeworld.com/lights/