Do I read right that you want to destroy it in place and then send a new one? Or you don't worry about the life time of the station as a whole, because you don't intend to play this game so long anymore?
Otherwise, maintenance life does not mean anything when it comes to 5-day failure rate. Your ship could just be so big that it will fail every turn anyway, or maybe you just have so small components (!) that a break does not consume so much maintenance, and thus will work for long. IFR is the most critical part to look for, but even if you could keep it lower than 1% (which is impossible on larger ships), it does not matter if you intend to tractor a ship on the end of its life cycle, because then the IFR will likely be over 100% in any case, thus rendering it immobile.
An example: I am currently testing two identical hangar design which have 4% IFR after clock 0.35, and already the tractor link breaks around every 10 5-day increments per model, which makes it really bothersome to fly them around. Just think how those will work after clock 10+...
I think at some size over over 10k or so, the only feasible 'military tug' would be a hangar ship with great range and maintenance life.
..Except for deployment, because there is this free time span before any ship starts making problems. Yet permanent tug without pause, or 'rescue tug' operations become impossible quickly.
