The old sliding gear transmissions are noisy, and as the previous post states, you will have to learn to double clutch which isn't that difficult. If you want the feel of a 70 year old vehicle, keep what you have. If you want something more like a more like a newer model, you will want to make some changes. The transmissions were very tough and if it always had oil in in it, it will probably last as long as you want to drive it.
