serviceLevel
Because its hardly mentioned, almost nobody knows what is does. Most people (Me included) always thought it brings the ship in mint condition again. That is not true. It only increases the service level by (4 + techLevel)%. The overhaul becomes offered in systems with techlevel > 6, when the service level drops below 85%. So, when you have a service level of only 75% and do maintenance at a level 7 system, your service level only rises by 11% to 86 %. That is just enough to not offer it a second time, but the next offer will come soon.
In the light that you only get a fixed amount of service, it is correct the the maintenance costs stay the same, but it still feels strange to the player who has no insight how much maintenance he gets. In trunk, I added a few days ago, a change that also makes the value dependent on the actual service level. It still sounds correct that repairing a bad maintained ship is more expensive than the same maintenance on a good maintained ship. It is just more work when working on bad maintained ships.
Result is that a Maintenance Overhaul now cost 25% more than in the past if you wait until it drops to 75% but the Maintenance Overhaul is actually cheaper when doing it immediately when it first becomes available.
A good thing about making it dependent on the service level is that it also fixes a (in my opinion) bug when also subentities were destroyed. In the past you payed for the subentity repair plus the full price for the service. Now, when you recently had done some maintenance, you don't pay twice for it, only for the subents.
(NB techLevels mentioned above are the one based techLevels, as seen by the player and not the internal zero based techLevels)