Hi Michael. There are lots of options. It depends what features you want.
I really like ARC as a home system. ARC Air has loads of features for laptiming and gameplay. I would suggest buying new - you always run a risk with something that is used and being sold no-returns. On your other thread I have made a few suggestions of clearing the short circuit.
An alternative to ARC Air is ARC One. This has fewer features - a lap timer plus pit stops for optional fuel and tyre simulations. Some users have used the ARC One unit as a stand-alone timer with a separate analogue power base. This mod is necessary: https://www.slotforum.com/forums/index.php?showtopic=77744
There is an older Scalextric C8215 lap counter. DS also have their DS-200 for high-end home use. Carrera have a lap timing bridge, which should work okay with a Scalextric layout.
For high-end home use and club tracks, there are systems like the DS-300 and Trackmate. Both can be used with various race management programs like Race Co-ordinator. A google search will take you to these and to various discussions on Slot car forums.
I hope that gets you started, but have a go with fixing your ARC Air - I like it very much and several of my club-mates have them. Not of us have had the problems you describe.