I use a mixture of simple green and a general purpose adhesive remover in a spray bottle.

Thanks @Robert Webb I’ll give that a try.

I use 409 cleaner on a soft rag.... if you don't leave it on too long it comes off easy.

Mothers VLR, vinyl leather rubber cleaner..
no harsh chemicals for me

Go-joe hand wipes takes it right off

First off, I make my lines as light as possible marking, so there is less cleaning to do after seeing. I Iike using Simple Green and a soft bristle scrub brush, but occasionally I have used mineral spirits on a soft cloth (damp, not dripping if course). As with any chemical used on vinyl or leather, I always test it on a scrap of the material being cleaned to make sure it is not doing more harm than good. Scrubbing with a soft brush in tight circular motion always helps get stuff out of the grain. KEEP IN MIND- always be extra careful when cleaning the area of a visable top stitch, pleat, etc because I've seen even space pen ink get into the thread and any moisture from the cleaner can make this even worse. My general rule is to always test it on a scrap (you may even put a stitch on the test peice) to make sure everything is copasetic. I hope this helps.

Rubbing alcohol or 3M Adhesive Remover seems to work well , but I've also cleaned it off w a magic eraser pad and some Simple Green.
I try not to get the lines on any part of the seat cover that will be visible after sewing it.

i dont know how you guys can pay what you do for space pens !!! I went to NASA a few months ago and they are even more expensive in there shop than ebay !! !! I get mine from china and pay £7.00 for 30

@Chris Vining you cant get the ones that actually went to space lol. I order mine only from somewhere overseas myself. Usually just price shop when I need more. So never the same place.

I buy them from Albright's...about $5.00 each....Maybe more $ than I can get them from across the pond, but it don't add much to the price of a job.....maybe a few cents? I can live with that.

I use the chinese refils from ebay 100 for £4.Even better than gel pen refils but a little more in cost are white water erasable fabric markers, cost is £2.50 for 5 from china.

@Keith Mayne do you have a link to the eBay refills?

I'm in the uk but if you search for "silver leather marking pen" you should get results. Also try "white water soluble pen" these are my main choice for marking as it wipes off easily, dries quicker than the gel pens(I find they tend to smear) and won't get in the thread.

@Keith Mayne thanks!

Windex has always worked for me and if it has been on there for a couple days use lighter fluid. The little bottles that you would refill a Zippo with. It has never hurt leather or vinly.

Do not use Ammonia-based cleansers such as Windex to clean vinyl.
While it won’t immediately affect the material, they will slowly break down petroleum-based vinyls, reducing it's lifespan.

Hi Keith, I'm in the UK, where do you get yours from bud?

No where in particular just the cheapest on ebay.Not sure if the refils are the same as the space pen but they work although it takes a while for them to dry and they smear a bit, I try to use them only in non visible areas.This is typical of what I use:- https://www.ebay.co.uk/itm/100pcs-Leather-Silver-Refillable-Pen-for-DIY-Cutting-Leather-Marking-Sliver/162791137066?hash=item25e71b9f2a:g:Jg4AAOSwihVb5bts
These are the same as the white chalk ones I use, again I just get the cheapest.I like these better as they dry quickly and clean off well.Again I try only to mark in non visible areas or where it will be covered with a top stitch.When they run out you can refresh them a bit by adding a drip of water down the end cap.I prefer these to the silver pens but are more expensive. https://www.ebay.co.uk/itm/5pcs-White-Water-Soluble-Pens-Erasable-Cross-Stitch-Fabric-Marker-Pens/163349745846?hash=item26086750b6:g:mnsAAOSw-eJb5ScC

I use Sprayaway Leather and vinyl cleaner. It wipes right off. https://www.amazon.com/Sprayway-SW990-Vinyl-Leather-Cleaner/dp/B0005JOH6E/ref=asc_df_B0005JOH6E/?tag=bingshoppinga-20&linkCode=df0&hvadid={creative}&hvpos={adposition}&hvnetw=o&hvrand={random}&hvpone=&hvptwo=&hvqmt=e&hvdev=c&hvdvcmdl={devicemodel}&hvlocint=&hvlocphy=&hvtargid=pla-4583520382460380&psc=1 Don't know why the link did this.